Solid electrolytic capacitor and manufacturing method

Abstract

Provided is a solid electrolytic capacitor in which a conductive polymer and an electrolyte solution are used together, and even if fibrillated fibers are included as a separator, an increase in equivalent series resistance in a high-temperature environment is suppressed, and a decrease in capacitance is suppressed. A solid electrolytic capacitor includes an anode body having a dielectric film, a cathode body facing the anode body, and an inter-electrode layer interposed between the anode body and the cathode body. The inter-electrode layer contains a conductive polymer, an electrolyte, and a separator. The separator contains fibrillated fibers and has an air permeability resistance of 5.8 (sec / 100 mL) or less. The conductivity of the inter-electrode layer is 55 (S) or more and less than 180 (S).

Description

Background Technology

[0001] Electrolytic capacitors consist of a valve-acting metal such as tantalum or aluminum as the anode and cathode foils. The anode foil is enlarged by shaping the valve-acting metal into a sintered body or etched foil, and a dielectric coating is applied to the enlarged surface. An electrolyte is present between the anode and cathode foils. The electrolyte is in close contact with the uneven surface of the anode foil, functioning as the actual cathode.

[0002] Capacitors are used in a variety of applications. For example, in the field of power electronics, in power supply circuits that convert AC power to DC power via a converter circuit and then convert the DC power back to the desired AC power via an inverter circuit, smoothing capacitors are used to suppress and smooth the DC output from the converter circuit before it is input to the inverter circuit. Additionally, decoupling capacitors are placed near semiconductor switching elements such as gallium nitride (GaN) to ensure stable operation and reduce noise. Furthermore, with the increasing power consumption in the field of power electronics, the demand for high-capacitance capacitors is increasing.

[0003] Furthermore, in recent years, electronic and electrical devices have become increasingly power-dependent due to applications such as rapid vehicle charging and increased electric motor drive power. If the equivalent series resistance (ESR) of a capacitor is high, the permissible ripple current is limited. Additionally, a high ESR results in a voltage drop during capacitor discharge and a voltage rise during capacitor charging, leading to voltage fluctuations. Therefore, capacitors with high ESR have reduced voltage smoothing capabilities. Consequently, there is a pressing need for capacitors with lower equivalent series resistance.

[0004] In this respect, electrolytic capacitors can increase their specific surface area by expanding the anode foil, giving them the advantage of easily achieving large capacitance compared to other types of capacitors such as film capacitors. Electrolytic capacitors contain electrolyte in the form of a liquid. The increased contact area between the electrolyte and the dielectric coating of the anode foil further facilitates the increase of capacitance.

[0005] In recent years, solid electrolytic capacitors, which use solid electrolytes with higher conductivity than electrolytes, have become increasingly common (see, for example, Patent Document 1). Solid electrolytic capacitors are small and have high capacitance; by using solid electrolytes with higher conductivity than electrolytes, they can achieve low equivalent series resistance (ESR). Manganese dioxide and 7,7,8,8-tetracyanoquinone dimethane (TCNQ) complexes are known as solid electrolytes.

[0006] In recent years, conductive polymers derived from monomers with π-conjugated double bonds, such as poly(3,4-ethylenedioxythiophene) (PEDOT), have rapidly gained popularity as solid electrolytes due to their slow reaction rates and excellent adhesion to dielectric coatings. Regarding conductive polymers, acidic compounds such as polyanions are used as dopants, and some monomer molecules possess partial structures that function as dopants, exhibiting high conductivity.

[0007] In addition to having low equivalent series resistance, solid electrolytic capacitors also have the advantages of preventing the electrolyte from evaporating and drying out over time, resulting in a long lifespan. However, in order to provide the dielectric coating with a repair function and reduce the leakage current of solid electrolytic capacitors, so-called hybrid solid electrolytic capacitors that combine conductive polymers and electrolytes are becoming increasingly popular (see, for example, Patent Document 2).

[0008] In recent years, due to the further development of the integration of electrical or electronic components, there is also a demand for miniaturization of solid electrolytic capacitors. Therefore, solid electrolytic capacitors require small size and high capacitance. As a result, the application of separators containing fibrillated fibers has been proposed (see, for example, Patent Documents 3 and 4).

[0009] Fibrous fibers are formed by, for example, pulping to branch from the surface of the original fibers into fine fibers. These fibrillated fibers intertwine with each other using these fine fibrillated fibers, thereby increasing the strength of the separator. Therefore, the separator thickness can be reduced. A thinner separator allows for larger anode and cathode foils within the solid electrolytic capacitor, contributing to an increase in the capacitor's capacitance. Therefore, from the viewpoint of achieving thinner thickness, fibrillated fibers are expected to further increase the capacitance of solid electrolytic capacitors.

[0010] Existing technical documents

[0011] Patent documents

[0012] Patent Document 1: Japanese Patent Application Publication No. 2011-60980

[0013] Patent Document 2: Japanese Patent Application Publication No. 2015-228424

[0014] Patent Document 3: Japanese Patent Application Publication No. 2010-245150

[0015] Patent Document 4: Japanese Patent Application Publication No. 2013-26536 Summary of the Invention

[0016] The problem that the invention aims to solve

[0017] However, Patent Document 4 points out that when using a separator containing fibrillated fibers, and measuring the gas density using a 6mm diameter cylinder as a gasket, the gas density exceeds 2.0 (sec / 100mL), hindering the uniform diffusion of the conductive polymer and resulting in 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 45.1mΩ even in the initial stage before the high-temperature load test.

[0018] Furthermore, when a solid electrolytic capacitor containing a fibrillated fiber was used in a solid electrolytic capacitor that combines a solid electrolyte and an electrolyte solution, the ESR of the solid electrolytic capacitor was found to increase even more when used in a high-temperature environment.

[0019] The present invention addresses the aforementioned problems and aims to provide a solid electrolytic capacitor and a manufacturing method thereof that, by combining a conductive polymer and an electrolyte, suppresses the increase in equivalent series resistance and the decrease in capacitance under high-temperature conditions, even when fibrillated fibers are used as separators.

[0020] Methods for solving problems

[0021] To address the aforementioned issues, the solid electrolytic capacitor of this embodiment includes: an anode having a dielectric coating, a cathode opposite to the anode, and an interelectrode layer between the anode and the cathode, comprising a conductive polymer, an electrolyte, and a separator, wherein the separator comprises fibrillated fibers and has a gas permeability resistance of 5.8 (sec / 100mL) or less, and the interelectrode layer has a conductivity of 55 (S) or more and less than 180 (S).

[0022] The air permeability resistance, also known as the Gurley value, is the time required for 100 mL of air to pass through the separator. Air permeability resistance is determined using the Gurley method according to JIS P8117:2009. A gasket with an inner diameter of 28.6 mm is used for measurement. However, when the air permeability resistance is within 1 (sec / 100 mL), a gasket with an inner diameter of 6 mm is used, and the value is converted to the value obtained using a 28.6 mm inner diameter gasket. Specifically, the value obtained using a 6 mm inner diameter gasket is multiplied by 6. 2 / 28.6 2 The conversion formula.

[0023] When applying this conversion formula, a breathability resistance of 2.0 (sec / 100mL) obtained with an inner diameter of 6mm translates to a breathability resistance of 0.09 (sec / 100mL) with an inner diameter of 28.6mm. Conversely, a breathability resistance of 5.8 (sec / 100mL) obtained with an inner diameter of 28.6mm translates to a breathability resistance of 132 (sec / 100mL) with an inner diameter of 6mm.

[0024] The conductivity can be made to 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.

[0025] The conductivity can be the reciprocal of the combined resistance of the conductive polymer, the electrolyte, and the separator.

[0026] The conductivity can be the reciprocal of the value obtained by subtracting the combined resistance of the anode lead terminal resistance, anode pin resistance, and anode body resistance (which are elements of anode resistance) and the cathode lead terminal resistance, cathode pin resistance, and cathode body resistance (which are elements of cathode resistance), i.e., the component resistance, from the ESR measured at the self-resonant frequency.

[0027] This allows the air permeability resistance of the separator to be below 5.5 (sec / 100mL).

[0028] This allows the air resistance of the separator to be 0.2 (sec / 100mL) or higher. A 0.2 (sec / 100mL) air resistance using a 28.6mm inner diameter gasket translates to a 4.5 (sec / 100mL) air resistance when the inner diameter is 6mm.

[0029] The conductivity of the interpolar layer can be made to be above 60 (S) and less than 180 (S).

[0030] The cathode body may have a cathode foil made of valve-acting metal and a conductive layer stacked on the cathode foil.

[0031] The conductivity of the interpolar layer can be made to be above 63 (S) and less than 180 (S).

[0032] The conductivity of the interpolar layer can be made to be above 63 (S) and less than 170 (S).

[0033] The interpolar layer can be formed by impregnating or dissolving the conductive polymer in a conductive polymer liquid.

[0034] To address the aforementioned issues, the method for manufacturing a solid electrolytic capacitor according to this embodiment includes: a step of forming an anode body having a dielectric coating, a step of forming a cathode body opposite to the anode body, and a step of forming an inter-electrode layer between the anode body and the cathode body, comprising a conductive polymer, an electrolyte, and a separator, wherein the inter-electrode layer uses the separator comprising fibrillated fibers and having a gas permeability resistance of 5.8 (sec / 100mL) or less, and the conductivity of the inter-electrode layer is adjusted to be 55 (S) or more and less than 180 (S).

[0035] The interpolar layer can be formed by impregnating a conductive polymer liquid that is dispersed or dissolved in the conductive polymer.

[0036] The effects of the invention

[0037] According to the present invention, in the case of solid electrolytic capacitors, by using conductive polymers and electrolytes together, even if fibrillated fibers are included as separators, the increase in equivalent series resistance under high temperature conditions is suppressed, and the decrease in capacitance is suppressed. Attached Figure Description

[0038] Figure 1 A scatter plot is shown to illustrate the ESR change rates of Examples 1 to 9 and Comparative Examples 1 to 3.

[0039] Figure 2 A scatter plot is shown to illustrate the rate of change of Cap for Examples 1 to 9 and Comparative Examples 1 to 3.

[0040] Figure 3 To illustrate the scatter plot of the ESR change rates of Examples 1 to 12 and Comparative Examples 1 to 4.

[0041] Figure 4 A scatter plot is shown to illustrate the rate of change of Cap for Examples 1 to 12 and Comparative Examples 1 to 4.

[0042] Figure 5 The bar chart shows the ESR change rate for Examples 1 to 12 and Comparative Examples 1 to 4.

[0043] Figure 6 The bar chart shows the rate of change of Cap for Examples 1 to 12 and Comparative Examples 1 to 4.

[0044] Figure 7 The diagram shows the connection positions of the anode lead terminals to the anode body and the cathode lead terminals to the cathode body.

[0045] Figure 8 The equivalent circuit diagram is shown to illustrate the resistance of a solid electrolytic capacitor. Detailed Implementation

[0046] The following describes the solid electrolytic capacitor and its manufacturing method according to the embodiments. It should be noted that the present invention is not limited to the embodiments described below.

[0047] (Solid electrolytic capacitor)

[0048] A solid electrolytic capacitor comprises a capacitor element. The capacitor element includes an anode, a cathode, and an inter-electrode layer. A dielectric coating is formed on the surface of the anode. The anode and cathode are positioned opposite each other, with the inter-electrode layer sandwiched between them. The inter-electrode layer is located between the dielectric coating of the anode and the cathode. This inter-electrode layer is composed of a conductive polymer, an electrolyte, and a separator.

[0049] The interelectrode layer is tightly bonded to the dielectric coating of the anode, functioning as the true cathode. The conductive polymer creates a conductive path between the anode and cathode through charge movement. The electrolyte creates a conductive path between the anode and cathode through ion movement. The separator, by loading the conductive polymer and electrolyte, forms the framework of the interelectrode layer and prevents short circuits between the anode and cathode.

[0050] This solid electrolytic capacitor is classified into wound type and laminated type. In the laminated type, the anode body and cathode body are alternately laminated with spacers in between. In the wound type, the anode body and cathode body are wound with spacers in between. In the wound type, the anode body, cathode body, and spacers are strip-shaped foils. In the wound type, the anode body, cathode body, and spacers are overlapped such that one end of the spacers and cathode body protrudes beyond one end of the anode body. Furthermore, the protruding spacers and cathode body are wound first to form a core, and then the layers of the anode body, cathode body, and spacers are wound around the core as a roll.

[0051] The anode lead terminals are connected to the anode body, and the cathode lead terminals are connected to the cathode body, extending outwards to the outside of the capacitor element. The anode and cathode lead terminals are electrically and mechanically connected to the anode and cathode bodies using methods such as cold soldering, pinning, ultrasonic welding, or laser welding. The solid electrolytic capacitor is electrically connected to the mounting circuit via these anode and cathode lead terminals. Through this connection to the mounting circuit, the solid electrolytic capacitor becomes a passive element that stores and discharges charge by obtaining capacitance through the dielectric polarization of the dielectric coating.

[0052] The capacitor element is housed in an outer casing with a bottom at one end and an opening at the other. The capacitor element is then sealed to the outer casing using a sealing body. The sealing body is fastened from the outside of the outer casing. After the capacitor element is sealed in the outer casing, the solid electrolytic capacitor undergoes an aging process to complete the manufacturing process.

[0053] (Interpolar layer)

[0054] The separator in the interpolar layer contains fibrillated fibers. These fibrillated fibers are formed by branching fine fibers from the surface of the original fibers, causing them to stand upright. The fibrillated fibers are formed, for example, by pulping. The air permeability resistance of the separator containing fibrillated fibers is 5.8 (sec / 100mL) or less.

[0055] Air resistance, also known as the Gurley value, is the time required for 100 mL of air to pass through the separator. Air resistance is determined using the Gurley method according to JIS P8117:2009. A 28.6 mm inner diameter gasket is used for measurement. However, when the air resistance is within 1 (sec / 100 mL), a 6 mm inner diameter gasket is used, and the value is converted to the value obtained with a 28.6 mm inner diameter gasket. Specifically, the value obtained with a 6 mm inner diameter gasket is multiplied by 6. 2 / 28.6 2 The conversion formula.

[0056] It should be noted that, based on this conversion formula, the air permeability resistance of 5.8 (sec / 100mL) obtained with an inner diameter of 28.6mm is converted to an air permeability resistance of 132 (sec / 100mL) with an inner diameter of 6mm.

[0057] Furthermore, the conductivity of the interelectrode layer is 55 (S) or higher and less than 180 (S). This conductivity is the reciprocal of the resistance of the interelectrode layer between the outermost surface of the anode and the outermost surface of the cathode. More specifically, the conductivity of the interelectrode layer is the reciprocal of the combined resistance of the conductive polymer, the electrolyte, and the separator.

[0058] As a method for calculating the conductivity of the interelectrode layer, the combined resistance of the element portion—comprising the anode lead terminal resistance, anode pin resistance, and anode body resistance (which are elements of anode resistance), and the cathode lead terminal resistance, cathode pin resistance, and cathode body resistance (which are elements of cathode resistance)—is subtracted from the ESR measured at the self-resonant frequency of the solid electrolytic capacitor. Regarding the self-resonant frequency, the phase difference between voltage and current at each frequency is measured; this is the frequency at which voltage and current are in phase. If it is the self-resonant frequency, the capacitive reactance (1 / ωC) and inductive reactance (ωL) become zero, allowing the ESR between the outermost surfaces of the anode and cathode to be obtained. In the frequency band where capacitance is also apparent deep within the expanded layer structures of the anode and cathode, it is necessary to consider the internal structure of the expanded layer and the concentration of conductive polymers within the expanded layer. Measuring the ESR at the self-resonant frequency simplifies the adjustment of the interelectrode layer conductivity.

[0059] Regarding the ESR measured at the self-resonant frequency of a solid electrolytic capacitor, it is first determined by the combined resistance of the anode and cathode leads, the anode pin resistance and cathode pin resistance, the anode body resistance and cathode body resistance, and the inter-electrode layer, which consists of resistive elements connecting the anode and cathode bodies every 1 mm along their length. The anode pin resistance and cathode pin resistance, being the pin connection resistances between the anode body and the anode lead terminals, and the cathode body and the cathode lead terminals, can be measured beforehand. The anode and cathode lead terminal resistances are fixed values ​​depending on the type of terminals. The anode body resistance and cathode body resistance are determined based on the type, length, and width of the anode and cathode bodies.

[0060] Secondly, to determine the combined resistance when these elements are shaped into capacitor components, the component shapes are assumed as follows. The connection point between the anode lead terminal and the anode body is set as the midpoint of the anode body, and the winding start length (representing the length from the start of winding the anode body to the connection point between the anode lead terminal and the anode body) is equal to the winding end length (representing the distance from the connection point between the anode lead terminal and the anode body to the end of winding the anode body). Regarding the connection point between the cathode lead terminal and the cathode body, when the cathode body overlaps the anode body, it is set to face the anode lead. Furthermore, the width of the cathode body is set to be the same as that of the anode body. The relationship between the connection points of the anode lead terminal and the anode body, and the connection points of the cathode lead terminal and the cathode body when the assumed components are unfolded is shown below. Figure 7 .

[0061] By utilizing an assumed element shape, the ESR of a solid electrolytic capacitor, measured at its self-resonant frequency, can be obtained using... Figure 8 The circuit diagram is shown. The resistance (Ω) of the anode lead terminal is R. al The resistance (Ω) of the anode pin is R. as The anode body resistance (Ω / mm) per 1 mm along the length direction is R. a The cathode lead resistance (Ω) is R. cl The cathode pin resistance (Ω) is R. cs The anode body resistance (Ω / mm) per 1 mm along the length direction is R. c The inter-electrode resistance (Ω) between the anode and cathode bodies every 1 mm along the length direction is R. p The length (mm) of the anode body in the longitudinal direction is L, and the starting length (mm) of the winding is l.

[0062] according to Figure 8 The circuit diagram shown indicates that the following mathematical equation (Equation 1) holds true for the ESR of a solid electrolytic capacitor measured at its self-resonant frequency. The R obtained by calculating the ESR from the following mathematical equation (Equation 1) is... pThe reciprocal of the product is used to calculate the conductivity of the interelectrode layer.

[0063] (Number 1)

[0064]

[0065] In this way, by using conductive polymers in conjunction with electrolytes, and by including fibrillated fibers as separators, the air permeability resistance is reduced to less than 5.8 (sec / 100mL), and the conductivity of the interelectrode layer is increased to more than 55 (S) and less than 180 (S), thereby achieving good capacitance and ESR in solid electrolytic capacitors.

[0066] That is, when the air permeability resistance is in a high range with an upper limit of 5.8 (sec / 100mL), the fibrillated fibers are entangled with fine fibrillated fibers, increasing the strength of the separator. Therefore, the thickness of the separator can be reduced. This reduction in separator thickness allows for an increase in the anode and cathode volume per unit volume, thereby increasing the capacitance of the solid electrolytic capacitor.

[0067] However, when using fibrillated fibers with high air permeability resistance as separators, the initial ESR of solid electrolytic capacitors generally increases significantly. In this regard, if the conductivity of the interelectrode layer is 55 (S) or higher but less than 180 (S), the interelectrode layer as a whole suppresses the increase in ESR, resulting in a low initial ESR even after long-term exposure to high temperatures. Furthermore, even with long-term exposure to high temperatures, capacitance degradation is also minimized. It should be noted that the initial ESR refers to the ESR of the solid electrolytic capacitor before exposure to high temperatures.

[0068] However, when the conductivity of the interelectrode layer is above 180 (S), the initial ESR is suppressed to a low level, and the rate of ESR change after long-term exposure to high temperatures is also suppressed to a low level. However, when the conductivity of the interelectrode layer is above 180 (S), the capacitance, which was beneficial due to high air permeability resistance, deteriorates sharply. If the conductivity of the interelectrode layer is less than 55 (S), the initial ESR of the solid electrolytic capacitor increases, and the rate of ESR change after long-term exposure to high temperatures also increases sharply.

[0069] Preferably, the conductivity of the interelectrode layer is less than 170 (S). If the conductivity is less than 170 (S), the rate of change in electrostatic capacitance after prolonged exposure to high temperature is further suppressed.

[0070] Furthermore, in the range where the air permeability resistance is greater than 5.8 (sec / 100mL), even if the conductivity of the interpolar layer is above 55 (S) but less than 180 (S), the rate of change of electrostatic capacity and the rate of change of ESR after long-term exposure to high temperature environment are drastically deteriorated.

[0071] Preferably, the air resistance is 0.2 (sec / 100mL) or higher. For an air resistance of 0.2 (sec / 100mL) or higher obtained with an inner diameter of 28.6mm, an air resistance of 0.2 (sec / 100mL) translates to an air resistance of 4.5 (sec / 100mL) with an inner diameter of 6mm.

[0072] If the air permeability resistance is less than 0.2 (sec / 100mL), then because the conductivity of the interlayer is in the range of 55 (s) to less than 180 (s), the ESR is still suppressed to a low level compared to the case where the interlayer is outside this conductivity range, but it enters the range where the ESR increases. However, if the air permeability resistance is 0.2 (sec / 100mL) or higher, then the air permeability resistance should increase compared to the range of less than 0.2 (sec / 100mL), but by combining this with the technical characteristic of the interlayer conductivity being 55 (s) to less than 180 (s), the rate of change in ESR is instead suppressed to a low level. Of course, because the air permeability resistance is increased, the rate of change in capacitance is also suppressed to a low level.

[0073] More preferably, the air permeability resistance of the separator containing fibrillated fibers is 5.8 (sec / 100mL) or less, and the conductivity of the interpolar layer is 60 (S) or more. If the conductivity of the interpolar layer is 60 (S) or more, the ESR change rate after long-term exposure to high temperature is further suppressed. Particularly preferably, the air permeability resistance of the separator containing fibrillated fibers is 5.8 (sec / 100mL) or less, and the conductivity of the interpolar layer is 63 (S) or more. If the conductivity of the interpolar layer is 63 (S) or more, the ESR change rate after long-term exposure to high temperature is particularly suppressed.

[0074] Regarding the air permeability resistance of the separator, the following methods can be appropriately combined to adjust it: The finer the average fiber diameter of the separator fibers, the greater the air permeability resistance. Increasing the proportion of fibrillated fibers in the separator also increases air permeability resistance. Increasing the thickness of the separator also increases air permeability resistance. Furthermore, increasing the flatness of the separator fiber shape also increases air permeability resistance. Due to differences in fiber shape and surface structure, the air permeability resistance varies depending on the type of fiber used in the separator. For example, compared to groups containing Manila hemp, esparto, and cotton, selecting fibers from groups containing kraft paper, synthetic fibers, and recycled fibers increases air permeability resistance. After the separator is formed into paper, it undergoes calendering, thereby increasing the air density of the separator.

[0075] Furthermore, the conductivity of the interlayer can be adjusted by appropriately combining the following methods: Reducing the gas permeability resistance of the separator increases conductivity. Increasing the solute concentration of the electrolyte increases conductivity. Choosing a solvent with good affinity for the electrolyte and a conductive polymer, and increasing the swelling degree of the conductive polymer, increases conductivity. For PEDOT:PSS, using a highly hydrophilic solvent with hydroxyl groups, such as ethylene glycol, diethylene glycol, or glycerol, adjust the ratio of the selected electrolyte solvent to the conductive polymer. Increasing the amount of conductive polymer attached per unit area of ​​the anode increases conductivity.

[0076] Decreasing the viscosity of the conductive polymer dispersion increases conductivity. Adding a high-boiling-point solvent to the conductive polymer dispersion also increases conductivity. Uniform penetration of the conductive polymer dispersion into the separator further increases conductivity. Specifically, by adjusting the depressurization or pressurization level when impregnating the element with the conductive polymer dispersion, a range can be established to achieve uniform penetration, depending on the composition of the conductive polymer dispersion and the characteristics of the separator, thus allowing for conductivity adjustment. Furthermore, when impregnating the capacitor element with the conductive polymer dispersion and then drying it, slow drying over a long period, or further drying with the adsorption of a high-boiling-point solvent, increases conductivity.

[0077] If multiple segments are formed in the dielectric coating of the anode body, the conductivity increases. These segments are formed by dividing the dielectric coating in the depth direction from the surface of the anode body towards the core, extending along the direction of the winding spool. These segments are formed by cracking the surface layer of the anode body, tearing the surface layer, forming a cut in the surface layer, cutting the surface layer, or digging into the surface layer. Examples of implementations of the segments include cracks, fissures, cuts, slits, or chisels. If segments are formed, the anode body easily follows the spool side when the capacitor element is wound, and the capacitor element is wound tightly. This tightness crushes the separators, increasing the conductivity of the inter-electrode layer. Therefore, the conductivity can be adjusted by regulating the number of segments, the groove width, the winding strength, etc.

[0078] (Separator)

[0079] The separators constituting the interpolar layer are cellulose and their mixtures, such as kraft paper, Manila hemp, esparto, hemp, and rayon; polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate and their derivatives; polytetrafluoroethylene resins, polyvinylidene fluoride resins, vinylon resins; aliphatic polyamides, semi-aromatic polyamides, and fully aromatic polyamides; polyimide resins; polyethylene resins; polypropylene resins; trimethylpentene resins; polyphenylene sulfide resins; acrylic resins; and polyvinyl alcohol resins, etc., which are used individually or in combination.

[0080] (Conductive polymer)

[0081] Conductive polymers are either self-doped conjugated polymers doped with intramolecular dopants or conjugated polymers doped with external dopants. Conjugated polymers are obtained by chemical oxidative polymerization or electrolytic oxidative polymerization of monomers or their derivatives having π-conjugated double bonds.

[0082] As a conjugated polymer, known conjugated polymers can be used without particular limitation. Examples include polypyrrole, polythiophene, polyfuran, polyaniline, polyacetylene, polyphenylene, polyphenylacetylene, poly(phenylene oxide), and polythiophene vinylene. These conjugated polymers can be used alone or in combination of two or more, and can be copolymers of two or more monomers.

[0083] Among the aforementioned conjugated polymers, conjugated polymers polymerized from thiophene or its derivatives are preferred, particularly those polymerized from 3,4-ethylenedioxythiophene (i.e., 2,3-dihydrothiophene[3,4-b][1,4]dioxin), 3-alkylthiophene, 3-alkoxythiophene, 3-alkyl-4-alkoxythiophene, 3,4-alkylthiophene, 3,4-alkoxythiophene, or their derivatives. As thiophene derivatives, compounds selected from thiophenes having substituents at the 3 and 4 positions are preferred, wherein the substituents at the 3 and 4 positions of the thiophene ring can form a ring together with the carbons at the 3 and 4 positions.

[0084] Dopant can be any known dopant without particular limitation. Dopant can be used alone or in combination of two or more. Additionally, polymers or monomers can be used. Examples of dopants include polyanionic and organic acids. Examples of polyanionic dopant include polyvinylsulfonic acid, polystyrene sulfonic acid, polyallyl sulfonic acid, polyacrylamide sulfonic acid, polymethacrylamide sulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, polyacrylic acid, polymethacrylic acid, and polymaleic acid.

[0085] As a conductive polymer, an example is poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid, which will be referred to as PEDOT:PSS below.

[0086] Conductive polymers can be formed within capacitor elements using conductive polymer liquids. The conductive polymer liquid is a dispersion or solution of conductive polymers. A wound body containing an anode and separator is impregnated with the conductive polymer liquid, thus confining the wound body. Additionally, the conductive polymer liquid is coated onto the anode body. The conductive polymer liquid can be impregnated or coated once or multiple times. The internal pressure of the wound body can be reduced, or alternatively, the conductive polymer liquid can be pressurized while impregnating the wound body.

[0087] The dispersion medium or solvent for conductive polymer liquids can be any medium in which conductive polymer particles or powders are dispersed or dissolved. The dispersion medium or solvent for conductive polymer liquids is water, or a mixture of water and an organic solvent. Examples of preferred organic solvents include polar solvents, alcohols, esters, hydrocarbons, carbonate compounds, ether compounds, chain ethers, heterocyclic compounds, and nitrile compounds.

[0088] For conductive polymer liquids, pH is adjusted to improve acidity by preventing the anode, cathode, and separator from dissolving. Additives can also be added as needed. If the pH is in the range of 2–9, the dissolution of the separator, anode, and cathode is inhibited. Examples of pH adjusters include ammonia, sodium hydroxide, primary amines, secondary amines, and tertiary amines. Examples of additives include organic binders, surfactants, dispersants, defoamers, coupling agents, antioxidants, and UV absorbers.

[0089] Polyols can be added to conductive polymer liquids as needed. Examples of polyols include sorbitol, ethylene glycol, diethylene glycol, triethylene glycol, polyoxyethylene glycol, glycerol, polyoxyethylene glycerol, xylitol, erythritol, mannitol, dipentaerythritol, pentaerythritol, or combinations of two or more of these. Because of their high boiling points, polyols remain in the conductive polymer layer after the drying process. Polyols can be used to alter the higher-order structure of the conductive polymer and to reorient the crystal structure of the polymer chains. Therefore, the use of polyols increases carrier mobility and the conductivity of the interlayer.

[0090] It should be noted that by taking measures to suppress the dissolution of the separator, and simultaneously immersing the wound body in a solution of monomers that become monomer units of conductive polymers and oxidants or supporting electrolytes, a polymerization reaction can be used to generate conductive polymers within solid electrolytic capacitors.

[0091] (Electrolyte)

[0092] The electrolyte is a solution obtained by adding a solute to a solvent. The solute is an organic acid or its salt, an inorganic acid or its salt, or a complex compound of organic and inorganic acids or its salt, and is an ionicly dissociable salt that dissociates into anionic and cationic components. The solvent can be used alone or in combination of two or more.

[0093] Organic acids whose solutes are anionic components include oxalic acid, succinic acid, glutaric acid, pimelic acid, octanoic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, maleic acid, adipic acid, benzoic acid, toluic acid, heptanoic acid, malonic acid, 1,6-decanedicarboxylic acid, 1,7-octanedicarboxylic acid, azelaic acid, resoric acid, 2,4,6-trihydroxybenzoic acid, gallic acid, gentisic acid, protocatechuic acid, pyrocatechuic acid, trimellitic acid, pyromellitic acid, and other carboxylic acids, phenols, and sulfonic acids. In addition, inorganic acids include boric acid, phosphoric acid, phosphorous acid, hypophosphite, carbonic acid, and silicic acid. Examples of compounds that are complex compounds of organic and inorganic acids include borosilicate, borosilicate oxalic acid, borosilicate diethanolic acid, borosilicate dimalonic acid, borosilicate disuccinic acid, borosilicate diadipic acid, borosilicate diazolic acid, borosilicate dibenzoic acid, borosilicate dimaleic acid, borosilicate dilactic acid, borosilicate dimalic acid, borosilicate ditartaric acid, borosilicate dicitric acid, borosilicate diphthalic acid, borosilicate di(2-hydroxy)isobutyric acid, borosilicate diresulfonic acid, borosilicate dimethylsalicylic acid, borosilicate dinaphtholic acid, borosilicate dimandelic acid, and borosilicate di(3-hydroxy)propionic acid.

[0094] In addition, salts of at least one of organic acids, inorganic acids, and complex compounds of organic and inorganic acids can include, for example, ammonium salts, quaternary ammonium salts, quaternary amidon salts, amine salts, sodium salts, potassium salts, etc. Quaternary ammonium ions, as quaternary ammonium salts, can include tetramethylammonium, triethylmethylammonium, tetraethylammonium, etc. Quaternary amidon salts can include ethyldimethylimidazolium, tetramethylimidazolium, etc. Amino salts can include salts of primary amines, secondary amines, and tertiary amines. Primary amines can include methylamine, ethylamine, propylamine, etc.; secondary amines can include dimethylamine, diethylamine, ethylmethylamine, dibutylamine, etc.; and tertiary amines can include trimethylamine, triethylamine, tributylamine, ethyldimethylamine, ethyldiisopropylamine, etc.

[0095] Regarding the solvent, it can be either a protic polar solvent or a non-protic polar solvent. Examples of protic polar solvents include monohydric alcohols, polyhydric alcohols, and oxyhydric alcohols. Examples of non-protic polar solvents include sulfones, amides, lactones, cyclic amides, nitriles, and sulfoxides.

[0096] Furthermore, other additives can be added to the electrolyte. Examples of additives include complexes of boric acid with polysaccharides (mannitol, sorbitol, etc.), complexes of boric acid with polyols, borate esters, nitro compounds, phosphate esters, and colloidal silica. These can be used individually or in combination of two or more. 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 can contain a polymeric solvent that acts as a voltage withstand enhancer. Examples of such polymeric solvents include polyols with added alkylene oxides or their derivatives.

[0097] Regarding the electrolyte, the capacitor element is immersed in the electrolyte, thereby impregnating the voids within the capacitor element. To impregnate the electrolyte within even finer voids, depressurization or pressurization can be performed as needed. The electrolyte impregnation process can be repeated multiple times. For example, the internal pressure of the capacitor element can be reduced, while the electrolyte is pressurized and injected into the capacitor element simultaneously.

[0098] (Anode)

[0099] The anode body, which is tightly sealed to the inter-electrode layer, is a foil made of a valve-acting metal, such as an anode foil. The foil can be formed by stretching the valve-acting metal or by sintering powdered valve-acting metal. Valve-acting metals include aluminum, tantalum, niobium, niobium oxide, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony.

[0100] An expansion layer is formed on one or both sides of the anode body. The expansion layer is an etched layer on which the foil has been etched, a sintered layer on which valve-acting metal powder has been sintered, or a vapor-deposited layer on which valve-acting metal particles have been vapor-deposited onto the foil. That is, the expansion layer has a porous structure, consisting of tunnel-like pits that are holes dug in the foil thickness direction, sponge-like pits that form an expanded sponge-like layer connected by small spatial gaps, or gaps between dense powders or particles.

[0101] The dielectric coating is formed on one or both sides of the anode body where the extended surface layer is formed. When an extended surface layer is formed, it is formed on the surface of the extended surface layer along its unevenness. 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 alumina layer formed by oxidizing the surface of the extended surface layer. In the chemical conversion process for forming the dielectric coating, a voltage is applied to the anode body in a chemical conversion solution with the desired withstand voltage as the target. The chemical conversion solution is a solution in which halide ions are absent, such as a phosphoric acid-based chemical conversion solution like ammonium dihydrogen phosphate, a boric acid-based chemical conversion solution like ammonium borate, or an adipic acid-based chemical conversion solution like ammonium adipic acid.

[0102] (Cathode)

[0103] The cathode is a foil made of a valve-acting metal, stretched into shape, such as a cathode foil. An expansion layer is formed on the cathode, similar to that on the anode. Plain foil without an expansion layer can also be used as the cathode. The cathode may have a natural oxide coating or a thin oxide coating of approximately 1–10 Vfs formed through chemical conversion treatment. The natural oxide coating is formed by the reaction of the cathode with oxygen in the air.

[0104] A conductive layer may be incorporated into the cathode body. The conductive layer is stacked on the cathode foil. If the cathode body includes a conductive layer that is in contact with the inter-electrode layer, the rate of change in ESR after prolonged exposure to high-temperature environments is suppressed even further, and the rate of change in capacitance is also suppressed even further.

[0105] As a conductive layer, it is sufficient to primarily contain inorganic materials or inorganic compounds. Examples of inorganic materials or inorganic compounds include titanium, zirconium, tantalum, niobium, their nitrides or carbides, aluminum carbide, carbon materials, and their composites or mixtures. Specifically, examples include conductive layers of carbon materials, conductive layers of titanium nitride, conductive layers of titanium carbide, conductive layers of a mixture of titanium and carbon materials, and conductive layers of a composite of aluminum carbide (Al4C3) and titanium oxide (TiO2).

[0106] Conductive layers containing carbon materials include, for example, graphite, carbon black, activated carbon, carbon nanotubes, fibrous carbon, or mixtures thereof. Examples of graphite include natural graphite, artificial graphite, and graphitized Kojtien black. Examples of carbon black include Kojtien black, acetylene black, channel black, and pyrolytic carbon black. Activated carbon uses materials derived from natural plant tissues such as coconut shells, synthetic resins such as phenolic resins, and fossil fuels such as coal, coke, and asphalt. Examples of fibrous carbon include carbon nanotubes and carbon nanofibers.

[0107] Methods for forming a carbon layer on a cathode foil include vacuum evaporation, sputtering, ion plating, CVD, coating, electroplating, and electroless plating. In the coating method, carbon material is dispersed in a dispersion solvent to prepare a slurry, which is then coated onto the cathode foil using methods such as slurry casting, doctor blade application, or spraying, and then dried. In the evaporation method, carbon material is evaporated by heating it in a vacuum with an electric current, or by irradiating it with an electron beam in a vacuum, thus forming a carbon film on the cathode foil. Furthermore, in the sputtering method, a target made of carbon material and a cathode foil are placed in a vacuum container, an inert gas is introduced into the vacuum container, a voltage is applied, and the plasma-generated inert gas collides with the target, causing carbon material particles knocked out from the target to deposit on the cathode foil.

[0108] After the conductive layer and cathode foil are stacked, a pressing process is preferably used for bonding. In the pressing process, for example, a pressure roller is used to clamp the cathode body, which consists of the conductive layer and the cathode foil, and a pressing line is applied. This allows the conductive layer to be pressed into the fine pores of the expanded surface layer through the pressing process, and also deforms the conductive layer along the uneven surface of the expanded surface layer. With this pressing structure, the adhesion between the conductive polymer and the conductive layer is improved, thus making it easier to constrain the ESR of the solid electrolytic capacitor using the conductivity of the inter-electrode layer.

[0109] The capacitor element is housed in an outer casing with a bottom at one end and an opening at the other. The capacitor element is then sealed to the outer casing using a sealing body. The sealing body is secured from the outside of the outer casing. After the capacitor element is sealed in the outer casing, the solid electrolytic capacitor undergoes an aging process to complete the manufacturing process. In the aging process, a DC voltage is applied to the solid electrolytic capacitor to repair defects in areas such as the dielectric coating.

[0110] Example

[0111] The solid electrolytic capacitors of the embodiments are described in more detail below. It should be noted that the present invention is not limited to the embodiments described below.

[0112] (Examples 1-9)

[0113] Solid electrolytic capacitors of Examples 1 to 9 and Comparative Examples 1 to 3 were fabricated. Examples 1 to 9 and Comparative Examples 1 to 3 used the same anode, separator, and electrolyte.

[0114] The anode body is an aluminum anode foil. The anode foil is etched to form an expanded layer consisting of sponge-like etch pits. Next, slits are formed on both sides of the etched anode foil using physical methods. Then, a dielectric coating is formed by chemically converting the anode foil with the slits. During the chemical conversion process, the anode foil is immersed in an ammonium adipate aqueous solution at 85°C, and a constant current of 2mA is applied while a voltage is maintained until the voltage reaches 65V.

[0115] The cathode body is formed by laminating a conductive layer onto an aluminum cathode foil. The cathode foils of Examples 1 to 8 and Comparative Examples 1 to 3 were etched to form an expanded surface layer consisting of sponge-like etch pits. Next, an oxide coating was formed by chemically converting the cathode foil. During the chemical conversion process, the cathode foil was immersed in an aqueous solution of ammonium adipate at 85°C, and a constant current of 2 mA was applied while a voltage was applied until the voltage reached 3V. Then, a conductive layer of titanium carbide (TiC) was deposited onto the cathode foil with the oxide coating using a vacuum arc evaporation method.

[0116] In Example 9, a conductive carbon layer is formed on the cathode body. The conductive layer is laminated onto the cathode foil by coating and drying a slurry containing carbon particles using a coating method, and then pressing it together using a pressing process.

[0117] Then, the anode lead terminal and the cathode lead terminal are connected to the anode body and the cathode body using pins. The anode body and the cathode body are overlapped and wound together through a separator to fabricate a capacitor element.

[0118] By including a conductive polymer liquid in the capacitor element, conductive polymer particles are attached to the dielectric coating of the anode foil, the cathode foil, and the separator. PEDOT:PSS particles are dispersed in the conductive polymer liquid. A conductive polymer liquid with a concentration consistent with the examples and comparative examples is prepared. The capacitor element is immersed in the conductive polymer liquid for 3 minutes under reduced pressure to below 30 kPa. After impregnation with the conductive polymer liquid, the wound is dried at room temperature for 10 minutes, and then dried at 120°C or 150°C.

[0119] Next, electrolytes conforming to the embodiments and comparative examples were prepared. The electrolytes were prepared by adding ammonium azelate to ethylene glycol. Regarding the details of the amount of ammonium azelate added, the amount of azelate was 0.2 mol / kg relative to the solvent, and the amount of ammonium ions was 0.2 mol / kg. Additionally, as additives, a total of 2 wt% of phosphate ester and p-nitrobenzoic acid were added to the electrolyte.

[0120] The capacitor element is then immersed in the electrolyte under reduced pressure. Next, the capacitor element is housed in an aluminum casing with a bottom at one end and an opening at the other. A sealing rubber seal is inserted into the opening of the aluminum casing, and the capacitor element is sealed by tightening the outer side of the casing.

[0121] Here, the solid electrolytic capacitors of Examples 1 to 9 and Comparative Examples 1 to 3 exhibit different interelectrode layer conductivity due to variations in the size of the capacitor element, the loading amount of the conductive polymer, the particle size of the conductive polymer, the composition of the conductive polymer liquid, and the number of impregnations of the conductive polymer liquid. Table 1 below shows the size of the capacitor element, the loading amount of the conductive polymer, the particle size of the conductive polymer, the composition of the conductive polymer liquid, the number of impregnations of the conductive polymer liquid, and the interelectrode layer conductivity of the capacitors of Examples 1 to 9 and Comparative Examples 1 to 3. The main solvent of the conductive polymer liquid is water, and the composition of the conductive polymer liquid shown in Table 1 is the proportion of ethylene glycol in the solvent.

[0122] (Table 1)

[0123]

[0124] The conductive polymer loading is calculated from the weight change of the capacitor element before and after impregnation with the conductive polymer liquid, the concentration of the conductive polymer in the conductive polymer liquid, and the surface area of ​​the anode body without considering the unevenness of the expansion layer. The surface area of ​​the anode body without considering the unevenness of the expansion layer is, in other words, the projected area when the anode body is projected along the foil thickness direction.

[0125] The conductivity was calculated as follows. First, the ESR of the solid electrolytic capacitors of Examples 1 to 9 and Comparative Examples 1 to 3 at their self-resonant frequencies was measured. The ESR was measured using an LCR meter (manufactured by NF Circuit Design Block, Agilent ZM2376). The ambient temperature during measurement was 25°C, the AC current level was set to a 1.0 Vrms sine wave, and the measurement frequency was set to the range of 1 Hz to 10 MHz. The phase difference between voltage and current at each frequency was measured, and the frequency at which voltage and current are in phase was defined as the self-resonant frequency. The self-resonant frequency of Examples 1 to 6 and Comparative Examples 1 and 2 was 500 kHz, the self-resonant frequency of Examples 7 and 8 was 300 kHz, and the self-resonant frequency of Examples 9 and Comparative Example 3 was 200 kHz.

[0126] Furthermore, the conductivity of the interelectrode layer in Examples 1 to 9 and Comparative Examples 1 to 3 was calculated by subtracting the reciprocal of the combined resistance of the anode lead terminal resistance, the anode pin resistance, and the anode body resistance (which are elements of anode resistance), and the cathode lead terminal resistance, the cathode pin resistance, and the cathode body resistance (which are elements of cathode resistance) from the ESR measurement results.

[0127] In Examples 1 to 6 and Comparative Examples 1 and 2, the combined resistance of the anode lead terminal resistance, anode pin resistance, and anode body resistance (which are elements of anode resistance), and the cathode lead terminal resistance, cathode pin resistance, and cathode body resistance (which are elements of cathode resistance), i.e., the component resistance, is 4.7 mΩ. In Examples 7 and 8, the component resistance is 4.9 mΩ. In Example 9, the component resistance is 5.2 mΩ. In Comparative Example 3, the component resistance is 4.7 mΩ.

[0128] (Characteristic Test 1)

[0129] The initial ESR, post-test ESR after 300 hours of exposure at 135°C, the rate of change of ESR relative to the initial ESR, and the rate of change of capacitance after 300 hours of exposure at 135°C were measured and calculated for the solid electrolytic capacitors of Examples 1 to 9 and Comparative Examples 1 to 3. ESR and capacitance (Cap) were measured using an LCR meter (manufactured by NF Circuit Design Block, Agilent ZM2376). The ambient temperature during measurement was 25°C, the AC current level was set to a 1.0 Vrms sine wave, and the measurement frequency was set to 120 Hz.

[0130] 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.

[0131] (Table 2)

[0132]

[0133] Based on Table 2 above, the ESR change rate and Cap change rate of Examples 1 to 9 and Comparative Examples 1 to 3 are shown in Table 2. Figure 1 and Figure 2 . Figure 1 The horizontal axis represents the conductivity of the interelectrode layer, and the vertical axis represents the ESR rate of change. Figure 2 The horizontal axis represents the conductivity of the interelectrode layer, and the vertical axis represents the rate of change of Cap.

[0134] As shown in Table 2 and Figure 1 As shown, in Comparative Examples 1 and 2, when fibrillated fibers were used as separators, the air resistance of a gasket with an inner diameter of 28.6 mm was 5.5 (sec / 100 mL), which translates to 125 (sec / 100 mL) for an inner diameter of 6 mm, significantly higher. Therefore, in Comparative Example 2, the initial ESR was 0.044 Ω, which is approximately 45 mΩ.

[0135] However, in Examples 1 to 9 and Comparative Example 3, fibrillated fibers with a permeability resistance of 5.5 (sec / 100mL) were used for the separator, but the conductivity of the interpolar layer was 55 (S) or higher, thus the initial ESR was suppressed to below 0.032 Ω. Furthermore, the maximum ESR change rate was +102% of that in Example 1. +102% is equivalent to the guaranteed range of ESR change rate, i.e., +100%. Even the ESR change rate of Example 1 was suppressed to approximately 56% of the ESR change rate of Comparative Example 2.

[0136] Furthermore, as shown in Table 2 above and Figure 2As shown, the Cap change rate of Examples 1 to 9 was also suppressed to a low level. However, Comparative Example 3, with an interpolar layer conductivity exceeding 180 (S), had a good initial ESR and a good ESR change rate, but its capacitance decreased significantly when exposed to high temperatures.

[0137] Thus, it was confirmed that if fibrillated fibers with a permeability of 5.5 (sec / 100mL) or less (5.8 (sec / 100mL) are used as separators, and the electrical conductivity of the interpolar layer is above 55 (S) and below 180 (S), the initial ESR becomes good, and the ESR change rate and Cap change rate after long-term exposure to high temperature environment are suppressed to a low level.

[0138] (Examples 10-12)

[0139] Furthermore, solid electrolytic capacitors of Examples 10 to 12 and Comparative Example 4 were fabricated. No conductive layer was formed in the cathode of Example 10. Another configuration of Example 10 was the same as that of Example 2. The element resistance of Example 10 was 4.2 mΩ, and the resonant frequency was 500 kHz. As a result, the conductivity of the interelectrode layer of Example 10 was close to 62 (S) of that of Example 2.

[0140] The separator in Example 11 is a mixture of fibrillated cellulose fibers and natural fibers, using a gasket with an inner diameter of 28.6 mm, resulting in an air resistance of 0.20 (sec / 100 mL). Another configuration of Example 11 is the same as that of Example 6. The element resistance of Example 11 is 6.1 mΩ, and the resonant frequency is 500 kHz. As a result, the conductivity of the interpolar layer in Example 11 is 69 (S).

[0141] In Example 12, the separator was fibrillated cellulose fiber, and the air resistance using a 28.6 mm inner diameter gasket was 5.7 sec / 100 mL. Another configuration of Example 12 was the same as that of Example 2. The element resistance of Example 12 was 4.2 mΩ, and the resonant frequency was 500 kHz. As a result, the conductivity of the interelectrode layer in Example 12 was close to 61 s of that in Example 2.

[0142] The separator in Comparative Example 4 was fibrillated cellulose fiber, and the air resistance using a gasket with an inner diameter of 28.6 mm was 5.9 (sec / 100 mL). Another configuration of Comparative Example 4 was the same as that 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 conductivity of the interpolar layer in Comparative Example 4 was close to 64 (S) of that in Example 2.

[0143] (Characteristic Test 2)

[0144] The initial ESR, post-test ESR after 300 hours of exposure at 135°C, the rate of change of ESR relative to the initial ESR, and the rate of change of capacitance after 300 hours of exposure at 135°C were measured and calculated for the solid electrolytic capacitors of Examples 10 to 12 and Comparative Example 4. The methods and conditions for measuring ESR and capacitance (Cap) were the same as those for Examples 1 to 9. The method for measuring the conductive polymer loading was the same as that for Examples 1 to 9.

[0145] The measurement results and calculation results of the rate of change of Examples 10 to 12 and Comparative Example 4 are shown together with those of Example 2 in Table 3 below. It should be noted that the separators of Examples 10 to 12 and Comparative Example 4 all contain fibrillated fibers.

[0146] (Table 3)

[0147]

[0148] Based on Table 3 above, the ESR and Cap change rates of Examples 10 to 12 and Comparative Example 4 are presented together with the ESR and Cap change rates of Examples 1 to 9 and Comparative Examples 1 to 3. Figure 3 and Figure 4 . Figure 3 The horizontal axis represents the conductivity of the interelectrode layer, and the vertical axis represents the ESR rate of change. Figure 4 The horizontal axis represents the conductivity of the interelectrode layer, and the vertical axis represents the rate of change of Cap. Furthermore, the rates of change of ESR and the rates of change of Cap for Examples 1 to 12 and Comparative Examples 1 to 4 are shown below. Figure 5 and Figure 6 That would be represented by a bar chart. Figure 5 The rate of change of ESR Figure 6 Cap represents the rate of change.

[0149] As shown in Table 3 above, Figures 3 to 6 As shown, the electrical conductivity of the interelectrode layer in Examples 2 and 10 is similar, and the air permeability resistance of the fibrillated fibers is also the same. Compared with Example 10, Example 2, which includes a conductive layer in the cathode body, exhibits particularly good ESR and Cap change rates.

[0150] Thus, it was confirmed that by forming an interface between the fibrillated fiber with high air permeability resistance and the cathode body in the conductive layer, the ESR change rate and Cap change rate can be well suppressed even when the solid electrolytic capacitor is exposed to a high temperature environment for a long time.

[0151] Additionally, as shown in Table 3 above, Figures 3 to 6As shown, in Example 12, where the air permeability resistance of the fibrillated fiber separator is 5.7 (sec / 100mL), the ESR change rate is close to 100%, and the Cap change rate remains within a good range. On the other hand, in Comparative Example 4, where the air permeability resistance of the fibrillated fiber separator is 5.9 (sec / 100mL), the ESR change rate is close to 150%, and the Cap change rate is nearly twice that of the other examples, indicating a decline.

[0152] This confirms that even if the air resistance of the separator containing fibrillated fibers is increased, 5.8 (sec / 100mL) is the upper limit.

[0153] Additionally, as shown in Table 2 above, Figures 3 to 6 As shown, the ESR change rate of Examples 2 to 9, with an interlayer conductivity of 60 (S) or higher, after long-term exposure to high-temperature environments was further suppressed by about 25% or more compared to Example 1. In particular, the ESR change rate of Examples 3 to 9, with an interlayer conductivity of 66 (S) or higher, after long-term exposure to high-temperature environments was further suppressed by about 35% or more compared to Example 1.

[0154] This confirms that the conductivity of the interelectrode layer is preferably 60 (S) or higher, and more preferably 63 (S) or higher.

[0155] In Example 11, if the conductivity of the interpolar layer is of interest, it is particularly good, with an ESR change rate of 69 (S) or higher, which is above 63 (S). However, the ESR change rate of Examples 4 and 5, whose interpolar layer conductivity is similar, remains around 60%, while the ESR change rate of Example 10 is 76%. The air permeability resistance of the fibrillated fiber separator in Example 11 is 0.20 (sec / 100mL).

[0156] This confirms that if the air resistance decreases to 0.2 (sec / 100mL) under an inner diameter of 28.6mm (equivalent to 4.5 (sec / 100mL) for an inner diameter of 6mm), then even if the conductivity of the interpolar layer is 60 (S) or higher but less than 180 (S), the ESR change rate increases. Therefore, it is confirmed that, preferably, the conductivity of the interpolar layer is 60 (S) or higher but less than 180 (S), and the air resistance of the separator containing fibrillated fibers is 0.2 (sec / 100mL).

Claims

1. A solid electrolytic capacitor, characterized in that, include: An anode body with a dielectric coating; The cathode body opposite to the anode body; And an interelectrode layer, comprising a conductive polymer, an electrolyte, and a separator, situated between the anode and the cathode. The separator comprises fibrillated fibers and has an air permeability resistance of less than 5.8 (sec / 100mL). The conductivity of the interpolar layer is greater than 55 (S) and less than 180 (S).

2. The solid electrolytic capacitor according to claim 1, characterized in that, The conductivity is the reciprocal of the resistance value of the inter-electrode layer between the outermost surface of the anode and the outermost surface of the cathode.

3. The solid electrolytic capacitor according to claim 1, characterized in that, The conductivity is the reciprocal of the combined resistance of the conductive polymer, the electrolyte, and the separator.

4. The solid electrolytic capacitor according to claim 1, characterized in that, The conductivity is the reciprocal of the component resistance obtained by subtracting the combined resistance of the anode lead terminal resistance, anode pin resistance, and anode body resistance (which are elements of anode resistance) and the cathode lead terminal resistance, cathode pin resistance, and cathode body resistance (which are elements of cathode resistance) from the ESR measured at the self-resonant frequency.

5. The solid electrolytic capacitor according to any one of claims 1 to 4, characterized in that, The air permeability resistance of the separator is less than 5.5 (sec / 100mL).

6. The solid electrolytic capacitor according to any one of claims 1 to 4, characterized in that, The air permeability resistance of the separator is above 0.2 (sec / 100mL).

7. The solid electrolytic capacitor according to any one of claims 1 to 4, characterized in that, The conductivity of the interpolar layer is greater than 60 (S) and less than 180 (S).

8. The solid electrolytic capacitor according to any one of claims 1 to 4, characterized in that, The cathode body has: a cathode foil made of valve-acting metal, and a conductive layer stacked on the cathode foil.

9. The solid electrolytic capacitor according to any one of claims 1 to 4, characterized in that, The conductivity of the interpolar layer is above 63 (S) and less than 180 (S).

10. The solid electrolytic capacitor according to any one of claims 1 to 4, characterized in that, The conductivity of the interpolar layer is above 63 (S) and less than 170 (S).

11. The solid electrolytic capacitor according to any one of claims 1 to 4, characterized in that, The interpolar layer is formed by impregnating a conductive polymer liquid that is dispersed or dissolved in the conductive polymer.

12. A method for manufacturing a solid electrolytic capacitor, characterized in that, include: The process of forming an anode body with a dielectric coating; The process of forming a cathode body opposite to the anode body; The process of forming an interelectrode layer comprising a conductive polymer, an electrolyte, and a separator, located between the anode and the cathode. The interpolar layer uses a separator comprising fibrillated fibers and having an air permeability resistance of 5.8 (sec / 100mL) or less. The conductivity of the interpolar layer is adjusted to be above 55 (S) and less than 180 (S).

13. The method for manufacturing a solid electrolytic capacitor according to claim 12, characterized in that, The interpolar layer is formed by impregnating a conductive polymer liquid that is dispersed or dissolved in the conductive polymer.

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