Solid electrolytic capacitor and manufacturing method

Abstract

The present invention provides a solid electrolytic capacitor in which a conductive polymer and an electrolyte solution are used in combination, an increase in equivalent series resistance in a high-temperature environment is suppressed even if fibrillated fibers are included as a separator, and a decrease in electrostatic capacity is suppressed. This solid electrolytic capacitor is provided with: an anode body that has a dielectric film; a cathode body that faces the anode body; and an inter-electrode layer that is interposed between the anode body and the cathode body. The inter-electrode layer includes a conductive polymer, an electrolyte solution, and a separator. The separator contains fibrillated fibers and has an air permeation resistance of 5.8 (sec / 100 mL) or less. The electric conductivity of the inter-electrode layer is not less than 55 (S) but less than 180 (S).

Description

Solid electrolytic capacitor and manufacturing method

[0001] Electrolytic capacitors have anode and cathode foils made of valve metals such as tantalum or aluminum. The anode foil is enlarged by shaping the valve metal into a sintered or etched foil, and the enlarged surface is coated with a dielectric film. An electrolyte is interposed between the anode and cathode foils. The electrolyte is in close contact with the irregular surface of the anode foil and functions as the true cathode.

[0002] Capacitors are used in a variety of applications. For example, in the field of power electronics, power from an AC power source is converted into DC power by a converter circuit, and this DC power is then converted into desired AC power by an inverter circuit. A smoothing capacitor is provided in a power supply circuit to suppress pulsation in the DC output from the converter circuit and smooth the DC before inputting it to the inverter circuit. Furthermore, a decoupling capacitor is provided near a semiconductor switching element such as a gallium nitride element to ensure stable operation of the semiconductor switching element and remove noise. Furthermore, with the trend toward higher power in the field of power electronics, there is a growing demand for capacitors with higher capacitance.

[0003] Furthermore, in recent years, electronic and electrical devices have become increasingly power-hungry, for example, due to applications such as rapid charging of vehicles and increased motor driving force. A high equivalent series resistance (ESR) of a capacitor limits the allowable ripple current. Furthermore, a high ESR of a capacitor causes a voltage drop due to the ESR when the capacitor is discharged, and a voltage increase due to the ESR when the capacitor is charged. In other words, the capacitor causes voltage fluctuations. Therefore, a capacitor with a high ESR has a low voltage smoothing capability. Therefore, a capacitor with a lower equivalent series resistance is desired.

[0004] In this regard, electrolytic capacitors have the advantage that the specific surface area can be increased by expanding the surface area of ​​the anode foil, making it easier to obtain a large capacitance compared to other types of capacitors such as film capacitors. Electrolytic capacitors contain an electrolyte in the form of an electrolytic solution. The contact area between the electrolytic solution and the dielectric film on the anode foil increases. This makes it easier to further increase the capacitance of electrolytic capacitors.

[0005] In recent years, solid electrolytic capacitors that use a solid electrolyte with higher conductivity than the electrolyte solution have also become popular (see, for example, Patent Document 1). Solid electrolytic capacitors are small and have large capacitance, and use a solid electrolyte with higher conductivity than the electrolyte solution, enabling low equivalent series resistance (ESR). Known solid electrolytes include manganese dioxide and 7,7,8,8-tetracyanoquinodimethane (TCNQ) complex.

[0006] In recent years, conductive polymers derived from monomers with π-conjugated double bonds, such as poly(3,4-ethylenedioxythiophene) (PEDOT), which has a slow reaction rate and excellent adhesion to dielectric films, have rapidly become popular as solid electrolytes. Conductive polymers use acid compounds such as polyanions as dopants, and the monomer molecules contain a partial structure that acts as a dopant, resulting in high conductivity.

[0007] In addition to having a low equivalent series resistance, solid electrolytic capacitors have the advantage of being long-lived, since there is no risk of the electrolyte drying up due to evaporation to the outside over time. However, so-called hybrid-type solid electrolytic capacitors that use both a conductive polymer and an electrolyte to repair defects in the dielectric film and reduce leakage current in solid electrolytic capacitors are also becoming popular (see, for example, Patent Document 2).

[0008] In recent years, with the further progress in the integration of electrical or electronic components, there has been a demand for miniaturization of solid electrolytic capacitors. Therefore, solid electrolytic capacitors are required to be small and have high capacitance. To address this, the use of separators containing fibrillated fibers has been proposed (see, for example, Patent Documents 3 and 4).

[0009] Fibrillated fibers are formed by, for example, beating thin fibers that branch out from the surface of the original fibers. The fibrillated fibers are entangled with each other using the fibrillated thin fibers, improving the strength of the separator. This allows the separator to be made thinner. A thinner separator allows the anode foil and cathode foil in a solid electrolytic capacitor to be made longer, contributing to an increase in the capacitance of the solid electrolytic capacitor. Therefore, from the perspective of enabling thinner separators, fibrillated fibers are expected to further increase the capacitance of solid electrolytic capacitors.

[0010] JP 2011-60980 A JP 2015-228424 A JP 2010-245150 A JP 2013-26536 A

[0011] However, Patent Document 4 points out that when a separator containing fibrillated fibers is used, the airtightness exceeds 2.0 (sec / 100 mL) when measured using a cylindrical aperture with a diameter of 6 mm as a gasket, which inhibits uniform diffusion of the conductive polymer and leads to a decrease in the capacitance and an increase in the ESR of the solid electrolytic capacitor. In particular, Comparative Example 6 of Patent Document 4 discloses an ESR value of 45.1 mΩ even in the initial stage before the high-temperature load test.

[0012] Furthermore, it was confirmed that when a separator containing fibrillated fibers is applied to a solid electrolytic capacitor that uses both a solid electrolyte and an electrolytic solution and the solid electrolytic capacitor is used in a high-temperature environment, the ESR of the solid electrolytic capacitor increases even more significantly.

[0013] The present invention has been proposed to solve the above-mentioned problems, and its purpose is to provide a solid electrolytic capacitor and a manufacturing method thereof in which an increase in equivalent series resistance in a high-temperature environment is suppressed and a decrease in capacitance is suppressed, even when a conductive polymer and an electrolyte solution are used in combination and a fibrillated fiber is included as a separator.

[0014] In order to solve the above-described problems, the solid electrolytic capacitor of the present embodiment includes an anode body having a dielectric coating, a cathode body facing the anode body, and an interelectrode layer interposed between the anode body and the cathode body and including a conductive polymer, an electrolyte solution, and a separator, wherein the separator includes fibrillated fibers and has an air resistance of 5.8 (sec / 100 mL) or less, and the interelectrode layer has an electrical conductivity of 55 (S) or more and less than 180 (S).

[0015] Here, the air permeability resistance is also called the Gurley value, and is the time required for 100 mL of air to permeate the separator. The air permeability resistance is measured by the Gurley method in accordance with JIS P8117:2009. A gasket with an inner diameter of 28.6 mm is used for the measurement. However, for those with an air permeability resistance of 1 (sec / 100 mL) or less, the measurement is performed using a gasket with an inner diameter of 6 mm and converted to a value measured with an inner diameter of 28.6 mm. Specifically, the value obtained with an inner diameter of 6 mm is multiplied by 6. ２ / 28.6 ２ Use the conversion formula to multiply by.

[0016] When this conversion formula is applied, the air resistance of 2.0 (sec / 100 mL) obtained with an inner diameter of 6 mm is converted to an air resistance of 0.09 (sec / 100 mL) with an inner diameter of 28.6 mm. Conversely, the air resistance of 5.8 (sec / 100 mL) obtained with an inner diameter of 28.6 mm is converted to an air resistance of 132 (sec / 100 mL) with an inner diameter of 6 mm.

[0017] The electrical conductivity may be the reciprocal of the resistance value of the inter-electrode layer between the outermost surface of the anode body and the outermost surface of the cathode body.

[0018] The electrical conductivity may be the reciprocal of a combined resistance of the conductive polymer, the electrolyte, and the separator.

[0019] The electrical conductivity may be the reciprocal of a value obtained by subtracting, from the ESR measured at the self-resonant frequency, the element portion resistance which is the combined resistance of the anode lead terminal resistance, the anode stitch resistance, and the anode body resistance which are anode resistance elements, and the cathode lead terminal resistance, the cathode stitch resistance, and the cathode body resistance which are cathode resistance elements, from the ESR measured at the self-resonant frequency.

[0020] The separator may have an air resistance of 5.5 (sec / 100 mL) or less.

[0021] The separator may have an air resistance of 0.2 (sec / 100 mL) or more. An air resistance of 0.2 (sec / 100 mL) using a gasket with an inner diameter of 28.6 mm is equivalent to an air resistance of 4.5 (sec / 100 mL) when used with an inner diameter of 6 mm.

[0022] The inter-electrode layer may have an electrical conductivity of 60 (S) or more and less than 180 (S).

[0023] The cathode body may include a cathode foil made of a valve metal, and a conductive layer laminated on the cathode foil.

[0024] The inter-electrode layer may have an electrical conductivity of 63 (S) or more and less than 180 (S).

[0025] The inter-electrode layer may have an electrical conductivity of 63 (S) or more and less than 170 (S).

[0026] The inter-electrode layer may be formed by being impregnated with a conductive polymer liquid in which the conductive polymer is dispersed or dissolved.

[0027] In order to solve the above problems, the solid electrolytic capacitor of the present embodiment includes the steps of: forming an anode body having a dielectric coating; forming a cathode body facing the anode body; and forming an interelectrode layer interposed between the anode body and the cathode body and including a conductive polymer, an electrolyte solution, and a separator; the interelectrode layer uses the separator that includes fibrillated fibers and has an air resistance of 5.8 (sec / 100 mL) or less, and the electrical conductivity of the interelectrode layer is adjusted to 55 (S) or more and less than 180 (S).

[0028] The inter-electrode layer may be formed by impregnation with a conductive polymer liquid in which the conductive polymer is dispersed or dissolved.

[0029] According to the present invention, a solid electrolytic capacitor uses a conductive polymer and an electrolyte solution in combination, and even if it contains fibrillated fibers as a separator, an increase in equivalent series resistance in a high-temperature environment is suppressed, and a decrease in capacitance is suppressed.

[0030] 1 is a scatter diagram showing the ESR change rates of Examples 1 to 9 and Comparative Examples 1 to 3. FIG. 2 is a scatter diagram showing the Cap change rates of Examples 1 to 9 and Comparative Examples 1 to 3. FIG. 3 is a scatter diagram showing the ESR change rates of Examples 1 to 12 and Comparative Examples 1 to 4. FIG. 4 is a scatter diagram showing the Cap change rates of Examples 1 to 12 and Comparative Examples 1 to 4. FIG. 5 is a bar graph of the ESR change rates of Examples 1 to 12 and Comparative Examples 1 to 4. FIG. 6 is a bar graph of the Cap change rates of Examples 1 to 12 and Comparative Examples 1 to 4. FIG. 7 shows the relationship between the connection position of the anode body lead terminal and the anode body, and the connection position of the cathode body lead terminal and the cathode body. FIG. 8 is an equivalent circuit diagram showing the resistance of a solid electrolytic capacitor.

[0031] Hereinafter, a solid electrolytic capacitor and a manufacturing method thereof according to an embodiment will be described, but the present invention is not limited to the embodiment described below.

[0032] (Solid electrolytic capacitor) A solid electrolytic capacitor includes a capacitor element. The capacitor element includes an anode body, a cathode body, and an interelectrode layer. A dielectric film is formed on the surface of the anode body. The anode body and the cathode body face each other with the interelectrode layer between them. The interelectrode layer is interposed between the dielectric film of the anode body and the cathode body. This interelectrode layer is composed of a conductive polymer, an electrolyte, and a separator.

[0033] The interelectrode layer is in close contact with the dielectric film of the anode body and functions as the true cathode. The conductive polymer creates a conductive path between the anode body and the cathode body through charge transfer. The electrolyte creates a conductive path between the anode body and the cathode body through ion transfer. The separator supports the conductive polymer and electrolyte, providing a framework for the interelectrode layer and preventing short circuits between the anode body and the cathode body.

[0034] These solid electrolytic capacitors are classified into wound type and laminated type. In laminated type, anode bodies and cathode bodies are alternately laminated with a separator sandwiched between them. In wound type, anode bodies and cathode bodies are wound with a separator sandwiched between them. In wound type, the anode bodies, cathode bodies, and separator are strip-shaped foil bodies. In wound type, the anode bodies, cathode bodies, and separator are overlapped so that one end of the separator and cathode body protrudes beyond one end of the anode body. Then, the protruding separator and cathode body are first wound to form a winding core, and the layers of anode bodies, cathode bodies, and separator are subsequently wound around the winding core as a winding axis.

[0035] An anode lead terminal is connected to the anode body, and a cathode lead terminal is connected to the cathode body, and these are extended outside the capacitor element. The anode lead terminal and cathode lead terminal are electrically and mechanically connected to the anode body and cathode body by cold welding, stitching, ultrasonic welding, laser welding, or the like. The solid electrolytic capacitor is electrically connected to the mounting circuit via these anode lead terminal and cathode lead terminal. By being electrically connected to the mounting circuit, the solid electrolytic capacitor becomes a passive element that obtains capacitance through the dielectric polarization of the dielectric film and stores and discharges electric charge.

[0036] The capacitor element is housed in an outer case that is closed at one end and open at the other end, and the capacitor element is sealed in the outer case with a sealing body that is crimped from the outside of the outer case. After the capacitor element is sealed in the outer case, the solid electrolytic capacitor undergoes an aging process to complete its production.

[0037] (Inter-polarity Layer) The separator of the inter-polarity layer contains fibrillated fibers. The fibrillated fibers are produced by fluffing thin fibers so that they branch from the surface of the original fibers. The fibrillated fibers are formed, for example, by beating. The air resistance of the separator containing the fibrillated fibers is 5.8 (sec / 100 mL) or less.

[0038] The air permeability resistance is also called the Gurley value, and is the time required for 100 mL of air to permeate the separator. The air permeability resistance is measured by the Gurley method in accordance with JIS P8117:2009. A gasket with an inner diameter of 28.6 mm is used for the measurement. However, for those with an air permeability resistance of 1 (sec / 100 mL) or less, the measurement is performed using a gasket with an inner diameter of 6 mm and converted to a value measured with an inner diameter of 28.6 mm. Specifically, the value obtained with an inner diameter of 6 mm is multiplied by 6. ２ / 28.6 ２ Use the conversion formula to multiply by.

[0039] Based on this conversion formula, when the air resistance of 5.8 (sec / 100 mL) obtained for an inner diameter of 28.6 mm is converted to an air resistance of 132 (sec / 100 mL) for an inner diameter of 6 mm.

[0040] The electrical conductivity of the interelectrode layer is equal to or greater than 55 (S) and less than 180 (S). The electrical conductivity of the interelectrode layer is the reciprocal of the resistance of the interelectrode layer between the outermost surface of the anode body and the outermost surface of the cathode body. Specifically, the electrical conductivity of the interelectrode layer is the reciprocal of the combined resistance of the resistance of the conductive polymer, the resistance of the electrolyte, and the resistance of the separator.

[0041] The electrical conductivity of the interelectrode layer is calculated by subtracting the element resistance, which is the combined resistance of the anode resistance elements (anode lead terminal resistance, anode stitch resistance, and anode body resistance) and the cathode resistance elements (cathode lead terminal resistance, cathode stitch resistance, and cathode body resistance), from the ESR measured at the self-resonant frequency of the solid electrolytic capacitor. The self-resonant frequency is determined by measuring the phase difference between the voltage and current at each frequency, and is the frequency at which the voltage and current are in phase. At the self-resonant frequency, the capacitive reactance (1 / ωC) and inductive reactance (ωL) become zero, allowing the ESR between the outermost surface of the anode body and the outermost surface of the cathode body to be determined. In frequency bands where capacitance is expressed deep within the anode body and cathode body expanded layer structures, the internal structure of the expanded layer and the density of the conductive polymer within the expanded layer must also be taken into account. Measuring the ESR at the self-resonant frequency simplifies the adjustment of the electrical conductivity of the interelectrode layer.

[0042] The ESR measured at the self-resonant frequency of a solid electrolytic capacitor is first calculated as the combined resistance of the anode lead terminal resistance and cathode lead terminal resistance, the anode stitch resistance and cathode stitch resistance, the anode body resistance and cathode body resistance, and the interelectrode layer resistance of the resistors connecting the anode body and cathode body every 1 mm in the longitudinal direction. The anode stitch resistance and cathode stitch resistance are the stitch connection resistance between the anode body and anode lead terminal and the stitch connection resistance between the cathode body and cathode lead terminal, and can be measured in advance. Here, the anode lead terminal resistance and cathode lead terminal resistance are constant values ​​depending on the type of terminal. The anode body resistance and cathode body resistance are determined by the type of anode body and cathode body and the length and width of the anode body and cathode body.

[0043] Next, to calculate the combined resistance when these are formed into the shape of a capacitor element, the element shape is assumed as follows. The connection position between the anode lead terminal and the anode body is the midpoint of the anode body, and the start of winding length, which indicates the distance from the start of winding the anode body to the connection position between the anode body lead terminal and the anode body, is assumed to be equal to the end of winding length, which indicates the distance from the connection position between the anode body lead terminal and the anode body to the end of winding the anode body. The connection position between the cathode lead terminal and the cathode body is assumed to face the anode stitch when the cathode body is placed over the anode body. The width direction length of the cathode body is also assumed to be the same as that of the anode body. Figure 7 shows the relationship between the connection positions between the anode body lead terminal and the anode body and the connection positions between the cathode body lead terminal and the cathode body when the assumed element is unfolded.

[0044] By using the assumed element shape, the ESR measured at the self-resonant frequency of the solid electrolytic capacitor can be shown in the circuit diagram of Figure 8. Here, the anode lead terminal resistance (Ω) is R ａｌ , anode stitch resistance (Ω) is R ａｓ , the anode resistance per 1 mm in the longitudinal direction (Ω / mm) is R ａ , the cathode lead resistance (Ω) is R ｃｌ , the cathode stitch resistance (Ω) is R ｃｓ , the anode resistance per 1 mm in the longitudinal direction (Ω / mm) is R ｃ The inter-electrode layer resistance (Ω) connecting the anode and cathode bodies for every 1 mm in the longitudinal direction is R ｐ The longitudinal length (mm) of the anode body is L, and the winding start length (mm) is 1.

[0045] From the circuit diagram shown in FIG. 8, the ESR measured at the self-resonant frequency of the solid electrolytic capacitor satisfies the following formula 1. ｐ The electrical conductivity of the inter-electrode layer can be determined by calculating the reciprocal of (Equation 1).

[0046] In this way, when a conductive polymer and an electrolyte solution are used in combination and fibrillated fibers are included as a separator, the capacitance and ESR of the solid electrolytic capacitor can be improved by setting the air resistance to 5.8 (sec / 100 mL) or less and the electrical conductivity of the interelectrode layer to 55 (S) or more and less than 180 (S).

[0047] That is, when the air permeation resistance is in a high range with an upper limit of 5.8 (sec / 100 mL), the fibrillated fibers are entangled with each other using the fine fibrillated fibers, improving the strength of the separator. This allows the separator to be made thinner. Reducing the separator thickness allows the anode body and cathode body per unit volume to be made longer and larger, improving the capacitance of the solid electrolytic capacitor.

[0048] However, when fibrillated fibers with high air permeability resistance are used for the separator, the initial ESR of the solid electrolytic capacitor generally increases significantly. In this regard, if the electrical conductivity of the inter-electrode layer is 55 (S) or more but less than 180 (S), the increase in ESR of the inter-electrode layer as a whole is suppressed, and the ESR of the solid electrolytic capacitor can be kept low, both in terms of the initial ESR and after long-term exposure to a high-temperature environment. Moreover, even if the solid electrolytic capacitor is exposed to a high-temperature environment for a long period of time, the degradation of capacitance can be kept low. The initial ESR is the ESR of the solid electrolytic capacitor before it is exposed to a high-temperature environment.

[0049] However, if the electrical conductivity of the inter-electrode layer is 180 (S) or higher, the initial ESR is kept low, and the ESR change rate after long-term exposure to a high-temperature environment is also kept low. However, if the electrical conductivity of the inter-electrode layer is 180 (S) or higher, the capacitance, which had been favorably affected by high air permeation resistance, rapidly deteriorates. If the electrical conductivity of the inter-electrode layer is less than 55 (S), the initial ESR of the solid electrolytic capacitor becomes high, and the ESR change rate after long-term exposure to a high-temperature environment also rapidly increases.

[0050] Preferably, the electrical conductivity of the inter-electrode layer is less than 170 (S). When the electrical conductivity is less than 170 (S), the rate of change in capacitance after long-term exposure to a high-temperature environment is further suppressed.

[0051] Furthermore, when the air permeation resistance is in the range of more than 5.8 (sec / 100 mL), even if the electrical conductivity of the inter-electrode layer is 55 (S) or more and less than 180 (S), the capacitance change rate and the ESR change rate after long-term exposure to a high-temperature environment rapidly deteriorate.

[0052] Preferably, the air resistance is 0.2 (sec / 100 mL) or more. This air resistance of 0.2 (sec / 100 mL) or more obtained with an inner diameter of 28.6 mm is converted to an air resistance of 4.5 (sec / 100 mL) with an inner diameter of 6 mm.

[0053] When the air permeation resistance is less than 0.2 (sec / 100 mL), the electrical conductivity of the inter-electrode layer is in the range of 55 (S) or more but less than 180 (S), so the ESR is still kept low compared to when the inter-electrode layer deviates from this electrical conductivity range, but the ESR enters a higher range. However, when the air permeation resistance is 0.2 (sec / 100 mL) or more, the air permeation resistance should be higher compared to when the inter-electrode layer is in the range of less than 0.2 (sec / 100 mL). However, when combined with the requirement that the electrical conductivity of the inter-electrode layer be 55 (S) or more but less than 180 (S), the fluctuation rate of the ESR is conversely kept low. Of course, as the air permeation resistance increases, the fluctuation rate of the capacitance is also kept low.

[0054] More preferably, the separator containing fibrillated fibers has an air resistance of 5.8 (sec / 100 mL) or less, and the inter-electrode layer has an electrical conductivity of 60 (S) or more. When the inter-electrode layer has an electrical conductivity of 60 (S) or more, the ESR change rate after long-term exposure to a high-temperature environment is further suppressed. Particularly preferably, the separator containing fibrillated fibers has an air resistance of 5.8 (sec / 100 mL) or less, and the inter-electrode layer has an electrical conductivity of 63 (S) or more. When the inter-electrode layer has an electrical conductivity of 63 (S) or more, the ESR change rate after long-term exposure to a high-temperature environment is particularly suppressed.

[0055] The air resistance of the separator can be adjusted by appropriately combining the following methods. That is, the thinner the average fiber diameter of the separator fibers, the higher the air resistance. The higher the proportion of fibrillated fibers in the separator, the higher the air resistance. The thicker the separator, the higher the air resistance. The higher the flatness of the separator fibers, the higher the air resistance. The air resistance varies depending on the type of separator fiber due to differences in fiber shape and surface structure. For example, selecting fibers from a group such as kraft, synthetic fiber, or recycled fiber rather than a group such as manila, esparto, or cotton increases the air resistance. The airtightness of the separator can be increased by calendering the separator after papermaking.

[0056] The electrical conductivity of the interelectrode layer can be adjusted by appropriately combining the following methods. That is, lowering the air resistance of the separator increases electrical conductivity. Increasing the solute concentration of the electrolyte increases electrical conductivity. Selecting an electrolyte solvent and conductive polymer with good affinity and increasing the degree of swelling of the conductive polymer increases electrical conductivity. For PEDOT:PSS, a highly hydrophilic solvent containing hydroxyl groups, such as ethylene glycol, diethylene glycol, or glycerin, is selected, and the content ratio of the selected electrolyte solvent and conductive polymer is adjusted. Increasing the amount of conductive polymer attached per unit area of ​​the anode body increases electrical conductivity.

[0057] The electrical conductivity increases as the viscosity of the conductive polymer dispersion decreases. The electrical conductivity increases as a high-boiling point solvent is added to the conductive polymer dispersion. The electrical conductivity increases as the conductive polymer dispersion is uniformly permeated into the separator. Specifically, by adjusting the degree of pressure reduction or pressure increase when the conductive polymer dispersion is impregnated into the element, a range exists in which the permeation can be made uniform depending on the composition of the conductive polymer dispersion and the characteristics of the separator, and the electrical conductivity can be adjusted. Furthermore, when the conductive polymer dispersion is impregnated into the capacitor element and the drying process is performed, the electrical conductivity increases if the conductive polymer dispersion is dried slowly over a long period of time or if a high-boiling point solvent is further applied before drying.

[0058] Forming multiple divisions in the dielectric coating of the anode body increases the electrical conductivity. The divisions divide the dielectric coating in the depth direction from the surface of the anode body toward the core and extend in the direction along the winding axis. The divisions are formed by cracking, splitting, slitting, notching, or digging into the surface layer of the anode body. That is, examples of actual divisions are cracks, fissures, slits, notches, or digging. When divisions are formed, the anode body is more likely to follow the winding axis when the capacitor element is wound, causing the capacitor element to be tightly wound. This tight winding crushes the separator and increases the electrical conductivity of the inter-electrode layer. Therefore, the electrical conductivity can be adjusted by adjusting the number of divisions, groove width, winding strength, etc.

[0059] (Separator) The separator constituting the inter-electrode layer is made of cellulose such as kraft, Manila hemp, esparto, hemp, rayon, and the like, and mixed papers thereof; polyester-based resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and derivatives thereof; polytetrafluoroethylene-based resins, polyvinylidene fluoride-based resins, vinylon-based resins; polyamide-based resins such as aliphatic polyamides, semi-aromatic polyamides, and wholly aromatic polyamides; polyimide-based resins, polyethylene resins, polypropylene resins, trimethylpentene resins, polyphenylene sulfide resins, acrylic resins, and polyvinyl alcohol resins; and these resins are used alone or in combination.

[0060] (Conductive polymer) Conductive polymer is a self-doped conjugated polymer doped with an intramolecular dopant or a conjugated polymer doped with an external dopant molecule. Conjugated polymers are obtained by chemical oxidative polymerization or electrolytic oxidative polymerization of a monomer having a π-conjugated double bond or a derivative thereof.

[0061] As the conjugated polymer, any known polymer can be used without any particular limitation. Examples include polypyrrole, polythiophene, polyfuran, polyaniline, polyacetylene, polyphenylene, polyphenylene vinylene, polyacene, polythiophene vinylene, etc. These conjugated polymers may be used alone or in combination of two or more types, or may even be a copolymer of two or more types of monomers.

[0062] Among the above conjugated polymers, preferred are conjugated polymers obtained by polymerizing thiophene or a derivative thereof, and preferred are conjugated polymers obtained by polymerizing 3,4-ethylenedioxythiophene (i.e., 2,3-dihydrothieno[3,4-b][1,4]dioxin), 3-alkylthiophene, 3-alkoxythiophene, 3-alkyl-4-alkoxythiophene, 3,4-alkylthiophene, 3,4-alkoxythiophene, or derivatives thereof. Preferred thiophene derivatives are compounds selected from thiophenes having substituents at the 3- and 4-positions, and the substituents at the 3- and 4-positions of the thiophene ring may form a ring together with the carbon atoms at the 3- and 4-positions.

[0063] Any known dopant can be used without any particular limitation. A single dopant may be used, or two or more dopants may be used in combination. A polymer or a monomer may also be used. Examples of dopants include polyanions and organic acids. Examples of polyanions include polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallylsulfonic acid, polyacrylsulfonic acid, polymethacrylic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprenesulfonic acid, polyacrylic acid, polymethacrylic acid, and polymaleic acid.

[0064] An example of the conductive polymer is poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid, and hereinafter this conductive polymer will be referred to as PEDOT:PSS.

[0065] The conductive polymer can be formed in the capacitor element using a conductive polymer liquid. The conductive polymer liquid is a dispersion or solution in which a conductive polymer is dispersed or dissolved. The wound body to which the anode body and separator are added is immersed in the conductive polymer liquid to impregnate the wound body with the conductive polymer liquid. Alternatively, the anode body is coated with the conductive polymer liquid. The conductive polymer liquid may be immersed or coated once or multiple times. The wound body may be impregnated with the conductive polymer liquid while reducing the pressure inside the wound body or, in addition, pressurizing the conductive polymer liquid.

[0066] The dispersion medium or solvent of the conductive polymer liquid may be any medium that disperses or dissolves conductive polymer particles or powder. The dispersion medium or solvent of the conductive polymer liquid is water or a mixture of water and an organic solvent. Suitable examples of the organic solvent include polar solvents, alcohols, esters, hydrocarbons, carbonate compounds, ether compounds, chain ethers, heterocyclic compounds, and nitrile compounds.

[0067] The pH of the conductive polymer solution is adjusted to improve acidity so that the anode body, cathode body, and separator do not dissolve, and additives may be added as needed. A pH in the range of 2 to 9 suppresses dissolution of the separator, anode body, and cathode body. Examples of pH adjusters include ammonia water, sodium hydroxide, primary amines, secondary amines, and tertiary amines. Examples of additives include organic binders, surfactants, dispersants, antifoaming agents, coupling agents, antioxidants, and ultraviolet absorbers.

[0068] The conductive polymer solution may contain a polyhydric alcohol, if necessary. Examples of polyhydric alcohols include sorbitol, ethylene glycol, diethylene glycol, triethylene glycol, polyoxyethylene glycol, glycerin, polyoxyethyleneglycerin, xylitol, erythritol, mannitol, dipentaerythritol, pentaerythritol, and combinations of two or more of these. Because of their high boiling points, polyhydric alcohols remain in the conductive polymer layer even after the drying process. The polyhydric alcohol changes the higher-order structure of the conductive polymer and reorients the crystalline structure of the polymer chains. Therefore, the polyhydric alcohol improves carrier mobility and the electrical conductivity of the interelectrode layer.

[0069] In addition, while taking measures to suppress dissolution of the separator, the wound body may be immersed in a solution of a monomer that will become a monomer unit of the conductive polymer and an oxidizing agent or a supporting electrolyte, and the conductive polymer may be formed by a polymerization reaction, thereby forming the conductive polymer in the solid electrolytic capacitor.

[0070] (Electrolyte) The electrolyte is a solution in which a solute is added to a solvent. The solute is an organic acid or a salt thereof, an inorganic acid or a salt thereof, or a composite compound of an organic acid and an inorganic acid or a salt thereof, and is an ion-dissociable salt that dissociates into an anion component and a cation component. The solvent may be used alone or in combination of two or more.

[0071] Examples of organic acids that serve as anionic solutes include carboxylic acids such as oxalic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, maleic acid, adipic acid, benzoic acid, toluic acid, enanthic acid, malonic acid, 1,6-decanedicarboxylic acid, 1,7-octanedicarboxylic acid, azelaic acid, resorcylic acid, phloroglucinic acid, gallic acid, gentisic acid, protocatechuic acid, pyrocatechuic acid, trimellitic acid, and pyromellitic acid, as well as phenols and sulfonic acids. Examples of inorganic acids include boric acid, phosphoric acid, phosphorous acid, hypophosphorous acid, carbonic acid, and silicic acid. Examples of the composite compound of an organic acid and an inorganic acid include borodisalicylic acid, borodioxalic acid, borodiglycolic acid, borodimalonic acid, borodisuccinic acid, borodiadipic acid, borodiazelaic acid, borodibenzoic acid, borodimaleic acid, borodilactic acid, borodimalic acid, boroditartaric acid, borodicitric acid, borodiphthalic acid, borodi(2-hydroxy)isobutyric acid, borodiresorcylic acid, borodimethylsalicylic acid, borodinaphthoic acid, borodimandelic acid, and borodi(3-hydroxy)propionic acid.

[0072] Furthermore, examples of at least one salt of an organic acid, an inorganic acid, or a complex compound of an organic acid and an inorganic acid include ammonium salts, quaternary ammonium salts, quaternized amidinium salts, amine salts, sodium salts, and potassium salts. Examples of quaternary ammonium ions of quaternary ammonium salts include tetramethylammonium, triethylmethylammonium, and tetraethylammonium. Examples of quaternized amidinium salts include ethyldimethylimidazolinium and tetramethylimidazolinium. Examples of amine salts include salts of primary amines, secondary amines, and tertiary amines. Examples of primary amines include methylamine, ethylamine, and propylamine. Examples of secondary amines include dimethylamine, diethylamine, ethylmethylamine, and dibutylamine. Examples of tertiary amines include trimethylamine, triethylamine, tributylamine, ethyldimethylamine, and ethyldiisopropylamine.

[0073] The solvent may be either a protic polar solvent or an aprotic polar solvent. Typical examples of protic polar solvents include monohydric alcohols, polyhydric alcohols, and oxyalcohol compounds. Typical examples of aprotic polar solvents include sulfones, amides, lactones, cyclic amides, nitriles, and sulfoxides.

[0074] Other additives may also be added to the electrolyte. Examples of such additives include complex compounds of boric acid and polysaccharides (e.g., mannitol, sorbitol), complex compounds of boric acid and polyhydric alcohols, borate esters, nitro compounds, phosphate esters, and colloidal silica. These may be used alone or in combination. The nitro compounds suppress the generation of hydrogen gas within the electrolytic capacitor. Examples of nitro compounds include o-nitrobenzoic acid, m-nitrobenzoic acid, p-nitrobenzoic acid, o-nitrophenol, m-nitrophenol, and p-nitrophenol. Furthermore, the electrolyte may contain a polymer solvent as a pressure resistance improver. Examples of such polymer solvents include polyols or derivatives thereof to which alkylene oxides have been added.

[0075] The capacitor element is immersed in the electrolyte solution, and the electrolyte solution is impregnated into the voids within the capacitor element. A depressurization or pressurization process may be performed as necessary to impregnate the electrolyte solution into smaller voids. The electrolyte solution impregnation process may be repeated multiple times. For example, the pressure inside the capacitor element may be reduced, and the electrolyte solution may be injected into the capacitor element while pressurizing the electrolyte solution.

[0076] (Anode Body) The anode body that is in close contact with the interelectrode layer is a foil made of a valve metal, such as an anode foil. The foil may be formed by stretching a valve metal or by sintering a valve metal powder. Valve metals include aluminum, tantalum, niobium, niobium oxide, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony.

[0077] A surface-expanding layer is formed on one or both sides of the anode body. The surface-expanding layer can be an etched layer formed by etching a foil, a sintered layer formed by sintering valve metal powder, or a vapor-deposited layer formed by vapor-depositing valve metal particles onto a foil. That is, the surface-expanding layer has a porous structure, consisting of tunnel-like pits dug in the thickness direction of the foil, spongy pits forming a sponge-like layer with a series of fine voids extending in a space, or voids between densely packed powder or particles.

[0078] The dielectric coating is formed on one or both sides of the anode body on which the surface-expanding layer is formed. When a surface-expanding layer is formed, it is formed on the surface of the surface-expanding layer, following the irregularities of the surface-expanding layer. The dielectric coating is typically an oxide coating formed on the surface of the anode body. If the anode body is made of aluminum, it is an aluminum oxide layer formed by oxidizing the surface of the surface-expanding layer. In the chemical conversion treatment to form the dielectric coating, a voltage is applied to the anode body in a chemical conversion solution until the desired withstand voltage is achieved. The chemical conversion solution is a solution free of halogen ions, such as a phosphoric acid-based chemical conversion solution such as ammonium dihydrogen phosphate, a boric acid-based chemical conversion solution such as ammonium borate, or an adipic acid-based chemical conversion solution such as ammonium adipate.

[0079] (Cathode body) The cathode body is a foil body made of a valve metal, for example, a cathode foil. A surface expansion layer is formed on the cathode body, just like the anode body. A plain foil without a surface expansion layer may also be used as the cathode body. The cathode body may have a natural oxide film or a thin oxide film of about 1 to 10 Vfs formed by chemical conversion treatment. The natural oxide film is formed when the cathode body reacts with oxygen in the air.

[0080] The cathode body may include a conductive layer. The conductive layer is laminated on the cathode foil. When the cathode body includes the conductive layer and the conductive layer is in contact with the inter-electrode layer, the rate of change in ESR after long-term exposure to a high-temperature environment is further reduced, and the rate of change in capacitance is also further reduced.

[0081] The conductive layer may contain mainly an inorganic substance or an inorganic compound. Examples of the inorganic substance or inorganic compound include titanium, zirconium, tantalum, niobium, nitrides or carbides thereof, aluminum carbide, carbon materials, and composites or mixtures thereof. Specific examples include a conductive layer of a carbon material, a conductive layer of titanium nitride, a conductive layer of titanium carbide, a conductive layer of a mixture of titanium and a carbon material, and aluminum carbide (Al ４ C ３ ) and titanium oxide (TiO ２ ) and a conductive layer combined therewith.

[0082] The conductive layer containing a carbon material includes, for example, graphite, carbon black, activated carbon, carbon nanohorn, fibrous carbon, or a mixture thereof as the carbon material. Examples of graphite include natural graphite, artificial graphite, and graphitized ketjen black. Examples of carbon black include ketjen black, acetylene black, channel black, and thermal black. Activated carbon is derived from natural plant tissues such as coconut husks, synthetic resins such as phenol, and fossil fuels such as coal, coke, and pitch. Examples of fibrous carbon include carbon nanotubes and carbon nanofibers.

[0083] Methods for forming a carbon layer on a cathode foil include vacuum deposition, sputtering, ion plating, CVD, coating, electrolytic plating, and electroless plating. In the coating method, a carbon material is dispersed in a dispersion solvent to prepare a slurry, which is then coated on the cathode foil by a slurry casting method, a doctor blade method, a spray atomization method, or the like, and dried. In the deposition method, the carbon material is evaporated by heating with electrical current in a vacuum, or by irradiating the carbon material with an electron beam in a vacuum, thereby forming a film of the carbon material on the cathode foil. In the sputtering method, a target made of a carbon material and the cathode foil are placed in a vacuum chamber, and an inert gas is introduced into the vacuum chamber and a voltage is applied, causing the plasmatized inert gas to collide with the target, and particles of the carbon material are knocked out of the target and deposited on the cathode foil.

[0084] After laminating the conductive layer and the cathode foil, they are preferably pressure-bonded by pressing. In the pressing, for example, the cathode body consisting of the conductive layer and the cathode foil is sandwiched between press rollers and a linear press pressure is applied. The pressing can be used to force the conductive layer into the pores of the surface-expanding layer and deform the conductive layer along the uneven surface of the surface-expanding layer. This pressure-bonding structure improves the adhesion between the conductive polymer and the conductive layer, making it easier to regulate the ESR of the solid electrolytic capacitor by the electrical conductivity of the inter-electrode layer.

[0085] The capacitor element is housed in an outer case that is closed at one end and open at the other, and the capacitor element is sealed in the outer case with a sealant. The sealant is crimped from the outside of the outer case. After the capacitor element is sealed in the outer case, the solid electrolytic capacitor undergoes an aging process to complete its production. In the aging process, a DC voltage is applied to the solid electrolytic capacitor to repair defects in the dielectric film, etc.

[0086] The solid electrolytic capacitors of the examples will be described in more detail below, but the present invention is not limited to the examples described below.

[0087] Examples 1 to 9 Solid electrolytic capacitors were fabricated according to Examples 1 to 9 and Comparative Examples 1 to 3. Examples 1 to 9 and Comparative Examples 1 to 3 used the same anode body, separator, and electrolyte.

[0088] The anode body was an aluminum anode foil. The anode foil was etched to form a surface-enlarging layer consisting of spongy etching pits. Next, a physical method was used to form a dividing section on the anode foil whose both sides had been etched. The anode foil with the dividing section formed thereon was then subjected to a chemical conversion treatment to form a dielectric film. During the chemical conversion treatment, the anode foil was immersed in an ammonium adipate aqueous solution at a liquid temperature of 85°C, and a voltage of 2 mA was applied until the voltage reached 65 V.

[0089] The cathode body was formed by laminating a conductive layer on an aluminum cathode foil. The cathode foils of Examples 1 to 8 and Comparative Examples 1 to 3 were subjected to an etching process to form a surface-enlarging layer consisting of spongy etching pits. The cathode foils were then subjected to a chemical conversion treatment to form an oxide film. During the chemical conversion treatment, the cathode foils were immersed in an ammonium adipate aqueous solution at a temperature of 85°C, and a constant current of 2 mA was applied until a voltage of 3 V was reached. Furthermore, a conductive layer of titanium carbide (TiC) was laminated on the cathode foil with the oxide film formed thereon by vacuum arc deposition.

[0090] A conductive layer of carbon was formed on the cathode body of Example 9. The conductive layer was laminated on the cathode foil by applying a slurry containing carbon particles by a coating method, drying the slurry, and pressing the slurry by a press.

[0091] An anode lead terminal and a cathode lead terminal were connected to the anode body and the cathode body by stitching. The anode body and the cathode body were stacked with a separator interposed therebetween and wound to prepare a capacitor element.

[0092] By impregnating this capacitor element with a conductive polymer solution, conductive polymer particles were attached to the dielectric film of the anode foil, the cathode foil, and the inside of the separator. PEDOT:PSS particles were dispersed in the conductive polymer solution. Conductive polymer solutions with conductive polymer concentrations appropriate for each example and comparative example were prepared. The conductive polymer solution was impregnated into the capacitor element for 3 minutes in an environment reduced in pressure to 30 kPa or less. After impregnation with the conductive polymer solution, the wound body was dried at room temperature for 10 minutes and then further dried at 120°C or 150°C.

[0093] Next, electrolyte solutions were prepared for each example and comparative example. The electrolyte solutions were prepared by adding ammonium azelaate to ethylene glycol. The amount of ammonium azelaate added was 0.2 (mol / kg) of azelaic acid and 0.2 (mol / kg) of ammonium ions relative to the solvent. Furthermore, as additives, a total of 2 wt % of phosphate ester and p-nitrobenzoic acid was added to the electrolyte solution.

[0094] The capacitor element was impregnated with these electrolytes. The capacitor element was immersed in the electrolyte, and the electrolyte was impregnated into the capacitor element under reduced pressure. The capacitor element was then housed in an aluminum case with one end closed and the other end open. A rubber seal was inserted into the opening of the aluminum case, and the outside of the aluminum case was crimped to seal the capacitor element.

[0095] The solid electrolytic capacitors of Examples 1 to 9 and Comparative Examples 1 to 3 have different electrical conductivities of the interelectrode layer depending on the size of the capacitor element, the amount of conductive polymer loaded, the particle size of the conductive polymer, the components of the conductive polymer solution, and the number of times of impregnation with the conductive polymer solution. The size of the capacitor elements, the amount of conductive polymer loaded, the particle size of the conductive polymer, the components of the conductive polymer solution, the number of times of impregnation with the conductive polymer solution, and the electrical conductivities of the interelectrode layer of Examples 1 to 9 and Comparative Examples 1 to 3 are shown in Table 1 below. The main solvent of the conductive polymer solution is water, and the components of the conductive polymer solution shown in Table 1 below are the percentage of ethylene glycol in the solvent.

[0096] (Table 1)

[0097] The amount of conductive polymer loaded was calculated from the change in weight of the capacitor element before and after impregnation with the conductive polymer solution, the conductive polymer concentration of the conductive polymer solution, and the apparent surface area of ​​the anode body without considering the unevenness of the surface-expanding layer. In other words, the apparent surface area of ​​the anode body without considering the unevenness of the surface-expanding layer is the projected area when the anode body is projected along the foil thickness direction.

[0098] The electrical conductivity was calculated as follows. First, the ESR at the self-resonant frequency of the solid electrolytic capacitors of Examples 1 to 9 and Comparative Examples 1 to 3 was measured. The ESR was measured using an LCR meter (Agilent ZM2376, manufactured by NF Corporation). The ambient temperature during measurement was 25°C, the AC current level was a sine wave of 1.0 Vrms, and the measurement frequency was in the range of 1 Hz to 10 MHz. The phase difference between the voltage and current at each frequency was measured, and the frequency at which the voltage and current were in phase was defined as the self-resonant frequency. The self-resonant frequencies of Examples 1 to 6 and Comparative Examples 1 and 2 were 500 kHz, the self-resonant frequencies of Examples 7 and 8 were 300 kHz, and the self-resonant frequencies of Example 9 and Comparative Example 3 were 200 kHz.

[0099] The electrolytic conductivity of the inter-electrode layer in Examples 1 to 9 and Comparative Examples 1 to 3 was calculated by obtaining the reciprocal of the value obtained by subtracting, from the ESR measurement results, the element portion resistance, which is the combined resistance of the anode lead terminal resistance, anode stitch resistance, and anode body resistance, which are anode resistance elements, and the cathode lead terminal resistance, cathode stitch resistance, and cathode body resistance, which are cathode resistance elements.

[0100] In Examples 1 to 6 and Comparative Examples 1 and 2, the element resistance, which is the combined resistance of the anode lead terminal resistance, anode stitch resistance, and anode body resistance, which are anode resistance elements, and the cathode lead terminal resistance, cathode stitch resistance, and cathode body resistance, which are cathode resistance elements, was 4.7 mΩ. In Examples 7 and 8, the element resistance was 4.9 mΩ. In Example 9, the element resistance was 5.2 mΩ. In Comparative Example 3, the element resistance was 4.7 mΩ.

[0101] (Characteristics Test 1) For the solid electrolytic capacitors of Examples 1 to 9 and Comparative Examples 1 to 3, the initial ESR, the post-test ESR after 300 hours of exposure to a temperature environment of 135°C, the ESR change rate of the post-test ESR relative to the initial ESR, and the capacitance change rate after 300 hours of exposure to a temperature environment of 135°C were measured and calculated. The ESR and capacitance (Cap) were measured using an LCR meter (Agilent ZM2376, manufactured by NF Corporation). The ambient temperature during measurement was 25°C, the AC current level was a sine wave of 1.0 Vrms, and the measurement frequency was 120 Hz.

[0102] The measurement results and calculation results of the rate of change for Examples 1 to 8 and Comparative Examples 1 to 3 are shown in Table 2 below. (Table 2)

[0103] Based on Table 2 above, the ESR change rates and Cap change rates for Examples 1 to 9 and Comparative Examples 1 to 3 are shown in Figures 1 and 2. The horizontal axis of Figure 1 represents the electrical conductivity of the inter-electrode layer, and the vertical axis represents the ESR change rate. The horizontal axis of Figure 2 represents the electrical conductivity of the inter-electrode layer, and the vertical axis represents the Cap change rate.

[0104] 1, in Comparative Examples 1 and 2, the fibrillated fibers were used in the separator, and the air resistance using a gasket with an inner diameter of 28.6 mm was 5.5 (sec / 100 mL), which is clearly high at 125 (sec / 100 mL) when converted to an inner diameter of 6 mm. Therefore, in Comparative Example 2 as well, the initial ESR was 0.044 Ω, or approximately 45 mΩ.

[0105] However, in Examples 1 to 9 and Comparative Example 3, fibrillated fibers with an air resistance of 5.5 (sec / 100 mL) were used for the separator, but the electrical conductivity of the inter-electrode layer was 55 (S) or higher, so the initial ESR was suppressed to 0.032 Ω or less. Moreover, the maximum ESR change rate was +102% of Example 1. +102% can be said to be equivalent to the guaranteed range of +100% ESR change rate. Even the ESR change rate of Example 1 was suppressed to approximately 56% of the ESR change rate of Comparative Example 2.

[0106] 2, the Cap change rate was also kept low in Examples 1 to 9. However, in Comparative Example 3, in which the electrical conductivity of the inter-electrode layer exceeded 180 (S), the initial ESR and the ESR change rate were both good, but when exposed to a high-temperature environment, the capacitance decreased significantly.

[0107] In this way, it was confirmed that when fibrillated fibers having an air resistance of 5.5 (sec / 100 mL) or less and 5.8 (sec / 100 mL) or less are used for the separator and the electrical conductivity of the inter-electrode layer is 55 (S) or more and 180 (S) or less, the initial ESR becomes good and the ESR change rate and the Cap change rate after long-term exposure to a high-temperature environment can be kept low.

[0108] (Examples 10-12) Furthermore, solid electrolytic capacitors of Examples 10 to 12 and Comparative Example 4 were fabricated. No conductive layer was formed on the cathode body of Example 10. The other configurations of Example 10 were the same as those of Example 2. The element resistance of Example 10 was 4.2 mΩ, and the resonant frequency was 500 kHz. As a result, the electrical conductivity of the inter-electrode layer of Example 10 was 62 (S), which is close to that of Example 2.

[0109] The separator of Example 11 was a mixture of fibrillated cellulose fibers and natural fibers, and the air permeation resistance using a gasket with an inner diameter of 28.6 mm was 0.20 (sec / 100 mL). The other configurations of Example 11 were the same as those of Example 6. The element resistance of Example 11 was 6.1 mΩ, and the resonant frequency was 500 kHz. As a result, the electrical conductivity of the inter-electrode layer of Example 11 was 69 (S).

[0110] The separator of Example 12 was made of fibrillated cellulose fibers, and the air permeation resistance using a gasket with an inner diameter of 28.6 mm was 5.7 (sec / 100 mL). Other configurations of Example 12 were the same as those of Example 2. The element resistance of Example 12 was 4.2 mΩ, and the resonant frequency was 500 kHz. As a result, the electrical conductivity of the inter-electrode layer of Example 12 was 61 (S), which is close to that of Example 2.

[0111] The separator of Comparative Example 4 was made of fibrillated cellulose fibers, and the air permeation resistance using a gasket with an inner diameter of 28.6 mm was 5.9 (sec / 100 mL). The other configurations of Comparative Example 4 were the same as those of Example 2. The element resistance of Comparative Example 4 was 4.2 mΩ, and the resonant frequency was 500 kHz. As a result, the electrical conductivity of the inter-electrode layer of Comparative Example 4 was 64 (S), which is close to that of Example 2.

[0112] (Characteristics Test 2) For the solid electrolytic capacitors of Examples 10 to 12 and Comparative Example 4, the initial ESR, the post-test ESR when exposed to a temperature environment of 135°C for 300 hours, the ESR change rate of the post-test ESR relative to the initial ESR, and the capacitance change rate when exposed to a temperature environment of 135°C for 300 hours were measured and calculated. The measurement methods and conditions for ESR and capacitance (Cap) were the same as in Examples 1 to 9. The measurement method for the amount of conductive polymer loaded was the same as in Examples 1 to 9.

[0113] The measurement results and calculation results of the rate of change for Examples 10 to 12 and Comparative Example 4, along with Example 2, are shown in Table 3 below. Note that the separators of Examples 10 to 12 and Comparative Example 4 all contain fibrillated fibers.

[0114] (Table 3)

[0115] Based on Table 3 above, the ESR change rates and Cap change rates of Examples 10 to 12 and Comparative Example 4 are shown in Figures 3 and 4, along with the ESR change rates and Cap change rates of Examples 1 to 9 and Comparative Examples 1 to 3. The horizontal axis of Figure 3 represents the electrical conductivity of the inter-electrode layer, and the vertical axis represents the ESR change rate. The horizontal axis of Figure 4 represents the electrical conductivity of the inter-electrode layer, and the vertical axis represents the Cap change rate. The ESR change rates and Cap change rates of Examples 1 to 12 and Comparative Examples 1 to 4 are also shown in bar graphs in Figures 5 and 6. Figure 5 represents the ESR change rate, and Figure 6 represents the Cap change rate.

[0116] 3 to 6, the electrical conductivity of the inter-electrode layer is similar and the air resistance of the fibrillated fibers is also similar in Example 2 and Example 10. Example 2, in which the cathode body is provided with a conductive layer, exhibits particularly good ESR change rate and Cap change rate compared to Example 10.

[0117] This confirmed that by forming a conductive layer at the interface between the fibrillated fibers with high air resistance and the cathode body, the ESR change rate and Cap change rate can be effectively suppressed even if the solid electrolytic capacitor is exposed to a high-temperature environment for a long period of time.

[0118] 3 to 6, in Example 12, in which the air resistance of the fibrillated fiber separator was 5.7 (sec / 100 mL), the ESR change rate was nearly 100%, and the Cap change rate remained within a good range. On the other hand, in Comparative Example 4, in which the air resistance of the fibrillated fiber separator was 5.9 (sec / 100 mL), the ESR change rate approached 150%, and the Cap change rate was nearly twice as poor as in the other Examples.

[0119] This confirmed that the upper limit of the air resistance of a separator containing fibrillated fibers was 5.8 (sec / 100 mL).

[0120] 3 to 6, in Examples 2 to 9 in which the inter-electrode layer has an electrical conductivity of 60 (S) or more, the ESR change rate after long-term exposure to a high-temperature environment is reduced by an additional 25% or more compared to Example 1. In particular, in Examples 3 to 9 in which the inter-electrode layer has an electrical conductivity of 66 (S) or more, the ESR change rate after long-term exposure to a high-temperature environment is reduced by an additional 35% or more compared to Example 1.

[0121] This confirmed that the electrical conductivity of the inter-electrode layer is preferably 60 (S) or more, and more preferably 63 (S) or more.

[0122] Here, in Example 11, focusing on the electrical conductivity of the inter-electrode layer, the ESR change rate is 69 (S) or higher, which is within a favorable range, being 63 (S) or higher. However, while the ESR change rates of Examples 4 and 5, which have similar electrical conductivities of the inter-electrode layer, remain in the 60% range, the ESR change rate of Example 10 is 76%. In Example 11, the air resistance of the fibrillated fiber separator is 0.20 (sec / 100 mL).

[0123] This confirmed that as the air permeation resistance decreased, and the air permeation resistance obtained at an inner diameter of 28.6 mm became 0.2 (sec / 100 mL), that is, the air permeation resistance converted to an inner diameter of 6 mm became 4.5 (sec / 100 mL), the ESR change rate increased even when the electrical conductivity of the inter-electrode layer was in the range of 60 (S) or more and less than 180 (S). Therefore, it was confirmed that the air permeation resistance of a separator containing fibrillated fibers, with an electrical conductivity of 60 (S) or more and less than 180 (S), is preferably 0.2 (sec / 100 mL).

Claims

1. A solid electrolytic capacitor comprising: an anode body having a dielectric film; a cathode body facing the anode body; and an interelectrode layer interposed between the anode body and the cathode body and including a conductive polymer, an electrolyte, and a separator; wherein the separator includes fibrillated fibers and has an air resistance of 5.8 (sec / 100 mL) or less; and the interelectrode layer has an electrical conductivity of 55 (S) or more and less than 180 (S).

2. The solid electrolytic capacitor according to claim 1, wherein the electrical conductivity is the reciprocal of a resistance value of the interelectrode layer between the outermost surface of the anode body and the outermost surface of the cathode body.

3. The solid electrolytic capacitor according to claim 1, wherein the electrical conductivity is the reciprocal of a combined resistance of the conductive polymer, the electrolyte, and the separator.

4. The solid electrolytic capacitor according to claim 1, wherein the electrical conductivity is the reciprocal of the ESR measured at the self-resonant frequency minus the element resistance, which is the combined resistance of the anode resistance elements, that is, the anode lead terminal resistance, the anode stitch resistance, and the anode body resistance, and the cathode resistance elements, that is, the cathode lead terminal resistance, the cathode stitch resistance, and the cathode body resistance.

5. The solid electrolytic capacitor according to any one of claims 1 to 4, wherein the separator has an air resistance of 5.5 (sec / 100 mL) or less.

6. The solid electrolytic capacitor according to any one of claims 1 to 4, wherein the separator has an air resistance of 0.2 (sec / 100 mL) or more.

7. The solid electrolytic capacitor according to any one of claims 1 to 4, wherein the electrical conductivity of the inter-electrode layer is 60 (S) or more and less than 180 (S).

8. The solid electrolytic capacitor according to any one of claims 1 to 4, wherein the cathode body comprises: a cathode foil made of a valve metal; and a conductive layer laminated on the cathode foil.

9. The solid electrolytic capacitor according to any one of claims 1 to 4, wherein the electrical conductivity of the interelectrode layer is 63 (S) or more and less than 180 (S).

10. The solid electrolytic capacitor according to any one of claims 1 to 4, wherein the electrical conductivity of the inter-electrode layer is 63 (S) or more and less than 170 (S).

11. The solid electrolytic capacitor according to any one of claims 1 to 4, wherein the inter-electrode layer is formed by impregnation with a conductive polymer liquid in which the conductive polymer is dispersed or dissolved.

12. A method for manufacturing a solid electrolytic capacitor comprising: a step of forming an anode body having a dielectric film; a step of forming a cathode body facing the anode body; and a step of forming an interelectrode layer interposed between the anode body and the cathode body and including a conductive polymer, an electrolyte, and a separator; wherein the interelectrode layer includes fibrillated fibers and has an air resistance of 5.8 (sec / 100 mL) or less, and the electrical conductivity of the interelectrode layer is adjusted to 55 (S) or more and less than 180 (S).

13. The method for producing a solid electrolytic capacitor according to claim 12, wherein the interelectrode layer is formed by impregnating the interelectrode layer with a conductive polymer liquid in which the conductive polymer is dispersed or dissolved.

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