Positive electrode body of solid electrolytic capacitor, solid electrolytic capacitor, method for manufacturing positive electrode body of solid electrolytic capacitor, and method for manufacturing solid electrolytic capacitor

Abstract

Provided are: a positive electrode body of a solid electrolytic capacitor that has a high withstand voltage and a low leakage current; a solid electrolytic capacitor; a method for manufacturing the positive electrode body of the solid electrolytic capacitor; and a method for manufacturing the solid electrolytic capacitor. This positive electrode body comprises: a valve action metal substrate; and a dielectric oxide film on the valve action metal substrate. The dielectric oxide film comprises: a void layer on a surface layer side of the dielectric oxide film; and a void repair layer on the side of the dielectric oxide film that interfaces with the valve action metal substrate. This positive electrode body is formed by first chemical conversion processing, void introduction processing, and second chemical conversion processing. In the first chemical conversion processing, a prescribed chemical conversion voltage is applied to the valve action metal substrate. In the void introduction processing, the positive electrode body is immersed in one or more of an acidic solution, an alkaline solution, and pure water. In the second chemical conversion processing, a chemical conversion voltage lower than that of the first chemical conversion treatment is applied.

Description

Anode body of solid electrolytic capacitor, solid electrolytic capacitor, method for manufacturing anode body of solid electrolytic capacitor, and method for manufacturing solid electrolytic capacitor

[0001] The present invention relates to an anode body for a solid electrolytic capacitor, a solid electrolytic capacitor, a method for manufacturing an anode body for a solid electrolytic capacitor, and a method for manufacturing a solid electrolytic capacitor.

[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 gallium nitride to ensure stable operation of the semiconductor switching element and remove noise.

[0003] With the recent trend toward higher power consumption, there is a growing demand for higher capacitance in capacitors. Electrolytic capacitors are easier to achieve higher capacitance than film capacitors, and are therefore more likely to meet this demand. Electrolytic capacitors use valve metals such as tantalum or aluminum as anode and cathode foils. 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 oxide film by anodizing or other processes. An electrolyte is interposed between the anode and cathode foils.

[0004] Electrolytic capacitors have a large capacitance and can meet the demand for higher capacity because the specific surface area of ​​the anode foil can be increased through the surface-expansion process. Furthermore, electrolytic capacitors contain an electrolyte in the form of an electrolytic solution. The electrolytic solution can penetrate the expanded surface of the anode foil, increasing the contact area with the dielectric oxide film. This allows the electrolytic capacitor to have a larger capacitance, making it suitable for meeting the demand for higher capacity associated with the recent trend toward higher power. However, the electrolyte evaporates and dissipates over time, causing the electrolytic capacitor to experience a decrease in capacitance and an increase in dissipation factor over time, resulting in drying out.

[0005] Therefore, among electrolytic capacitors, solid electrolytic capacitors using solid electrolytes have been attracting attention. Solid electrolytic capacitors are free from or suppress the effects of drying up of the electrolyte. In addition, solid electrolytic capacitors have the advantage of low equivalent series resistance (ESR).

[0006] Known solid electrolytes include manganese dioxide and 7,7,8,8-tetracyanoquinodimethane (TCNQ) complexes. 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 oxide 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] JP 2003-160647 A JP 2008-258224 A

[0008] On the other hand, in some fields such as power electronics, capacitors with high withstand voltages are expected. For example, smoothing capacitors with a withstand voltage of 470 V are used in inverters for driving motors installed in electric vehicles, but smoothing capacitors with even higher withstand voltages are also expected to achieve even faster charging. Electrolytic capacitors using an electrolyte solution have a high withstand voltage due to the defect repair function of the electrolyte solution in the dielectric oxide film, but even such electrolytic capacitors do not easily meet the high withstand voltage requirement.

[0009] Furthermore, solid electrolytic capacitors are less able to withstand high voltages than electrolytic capacitors using an electrolytic solution due to the need for adhesion to the anode foil and the ability to repair defects in the dielectric oxide film. Generally, increasing the thickness of the dielectric oxide film is considered to increase the withstand voltage of a capacitor. However, even if the dielectric oxide film is thickened, it is difficult for solid electrolytic capacitors to achieve a withstand voltage of more than 400 V. In fact, even the capacitance, which is an advantage of solid electrolytic capacitors, is significantly reduced.

[0010] Figure 20 is a graph showing the relationship between the formation voltage for forming a dielectric oxide film and the breakdown voltage in a solid electrolytic capacitor. As shown in Figure 20, the relationship between the breakdown voltage and the formation voltage is well proportional up to a breakdown voltage of 300 V. However, to impart a breakdown voltage of 350 V or more to a solid electrolytic capacitor, a formation voltage significantly exceeding the breakdown voltage is required. To impart a breakdown voltage of 470 V to a solid electrolytic capacitor, a large formation voltage exceeding 1000 V is required. It appears difficult to achieve a breakdown voltage of 500 V by increasing the formation voltage.

[0011] In other words, it has not been easy to achieve a high withstand voltage in solid electrolytic capacitors that can handle the increasing power demands of recent years. Therefore, current solid electrolytic capacitors are mainly capable of withstanding voltages of around 100 V at most, and in fields where a withstand voltage of over 400 V is desired, solid electrolytic capacitors are not an option, even if they have a long life and low equivalent series resistance, because the power required for production is too great.

[0012] Furthermore, solid electrolytic capacitors have a leakage current, and if a large leakage current occurs in a high-voltage circuit, not only will the solid electrolytic capacitor deteriorate more quickly, but in the worst case scenario, the circuit may be destroyed.

[0013] The present invention has been proposed to solve the above-mentioned problems, and an object of the present invention is to provide an anode body for a solid electrolytic capacitor having a high withstand voltage and low leakage current, a solid electrolytic capacitor, a method for manufacturing an anode body for a solid electrolytic capacitor, and a method for manufacturing a solid electrolytic capacitor.

[0014] In order to solve the above-mentioned problems, the anode body of the solid electrolytic capacitor of this embodiment is an anode body for a solid electrolytic capacitor, and includes a valve metal substrate and a dielectric oxide film on the valve metal substrate, and the dielectric oxide film has a void layer on the surface side of the dielectric oxide film and a void repair layer on the boundary side of the dielectric oxide film with the valve metal substrate.

[0015] In order to solve the above-described problems, the solid electrolytic capacitor of this embodiment includes an anode body, a cathode body, and a solid electrolyte layer. The anode body has a valve metal substrate and a dielectric oxide film on the valve metal substrate. The dielectric oxide film has a void layer on a surface side of the dielectric oxide film and a void repair layer on a boundary side of the dielectric oxide film with the valve metal substrate.

[0016] The solid electrolyte layer may include polyethylenedioxythiophene doped with polystyrene sulfonic acid, and the void repair layer may have a withstand voltage of 400 V or less.

[0017] The anode body may have a hydrated oxide film on the surface thereof, the surface being more superficial than the dielectric oxide film.

[0018] In order to solve the above-described problems, the method for manufacturing an anode body for a solid electrolytic capacitor according to the present embodiment includes: a first chemical conversion treatment in which a predetermined chemical conversion voltage is applied to a valve metal base material; a void introduction treatment in which, after the first chemical conversion treatment, the anode body is immersed in any one or more of an acidic solution, an alkaline solution, and pure water; and a second chemical conversion treatment in which, after the void introduction treatment, a chemical conversion voltage lower than that of the first chemical conversion treatment is applied.

[0019] Furthermore, in order to solve the above-described problems, a method for manufacturing a solid electrolytic capacitor according to the present embodiment is a method for manufacturing a solid electrolytic capacitor including an anode body, a cathode body, and a solid electrolyte layer that have valve action metal as a base material, and includes an anode body processing step of processing the anode body, and an element forming step of incorporating the anode body, the cathode body, and the solid electrolyte layer to form a capacitor element, wherein the anode body processing step includes a first chemical conversion treatment of applying a predetermined chemical conversion voltage to a valve action metal base material, a void introduction treatment of immersing the anode body in any one or more of an acidic solution, an alkaline solution, and pure water after the first chemical conversion treatment, and a second chemical conversion treatment of applying a chemical conversion voltage lower than that of the first chemical conversion treatment after the void introduction treatment.

[0020] The second chemical conversion treatment may be performed by applying a chemical conversion voltage that is less than 90% of that applied in the first chemical conversion treatment.

[0021] In the element forming step, the solid electrolyte layer containing polyethylenedioxythiophene doped with polystyrene sulfonic acid may be incorporated into the capacitor element, and the second chemical conversion treatment in the anode body processing step may be performed by applying a chemical conversion voltage of 400 V or less.

[0022] The first chemical conversion treatment forms a dielectric oxide film on the valve metal substrate, the void introduction treatment forms a void layer on the surface side of the dielectric oxide film, and the second chemical conversion treatment forms a void repair layer of the dielectric oxide film on the boundary side of the valve metal substrate.

[0023] Before the first chemical conversion treatment, a hot water treatment may be performed in which the valve metal substrate is immersed in hot water.

[0024] The element forming step may include incorporating the anode body that has been subjected to the second chemical conversion treatment into the capacitor element.

[0025] In the element formation step, the anode body, after the first chemical conversion treatment and the void introduction treatment have been completed and before the second chemical conversion treatment has been performed, may be incorporated into the capacitor element, and the second chemical conversion treatment may be performed after the solid electrolyte layer has been incorporated into the capacitor element by the element formation step.

[0026] According to the present invention, it is possible to increase the withstand voltage of a solid electrolytic capacitor and reduce the leakage current of the solid electrolytic capacitor.

[0027] 1 is a schematic diagram showing an anode body of a solid electrolytic capacitor; FIG. 2 is a flowchart showing a method for manufacturing an anode body of a solid electrolytic capacitor; FIG. 3 is a flowchart showing a method for manufacturing a solid electrolytic capacitor; FIG. 4(a) is an STEM photograph of Comparative Example 1 and an STEM photograph of Comparative Example 2; FIG. 4(b) is an SEM photograph of Example 1; FIG. 4(b) is an SEM photograph of Example 2; FIG. 4(b) is an SEM photograph of Comparative Example 3; FIG. 4(a) is a graph showing the relationship between applied voltage and leakage current of Comparative Example 1, and FIG. 4(b) is a graph showing the relationship between applied voltage and leakage current of Comparative Example 2; FIG. 4(b) is a graph showing the relationship between applied voltage and leakage current of Example 1; FIG. 4(b) is a graph showing the relationship between applied voltage and leakage current of ... Comparative Example 3; FIG. 4(b) is an STEM photograph of Example 3; FIG. 4(b) is a graph showing the element ratio of sulfur at each depth of an anode body of Example 3; FIG. 4(b) is a graph showing the relationship between applied voltage and leakage current of Example 3; 1 is a graph showing the relationship between applied voltage and leakage current for Comparative Examples 6 and 7 and Examples 7 to 9. 2 is a graph showing the relationship between applied voltage and leakage current for Comparative Examples 8 and 9 and Examples 10 to 12. 3 is a graph showing the relationship between applied voltage and leakage current for Comparative Examples 10 and 11 and Examples 13 to 15. 4 is a graph showing the relationship between formation voltage and withstand voltage in a solid electrolytic capacitor.

[0028] (Solid Electrolytic Capacitor) A solid electrolytic capacitor includes an anode body, a cathode body, and a solid electrolyte layer made of a conductive polymer, and does not contain an electrolytic solution. The anode body and the cathode body are arranged opposite each other. A separator is interposed between the anode body and the cathode body. Solid electrolytic capacitors are classified into, for example, stacked, wound, and flat types depending on their shape. In stacked types, anode bodies and cathode bodies are alternately stacked with a separator sandwiched between them. In wound types, anode bodies and cathode bodies are wound with a separator sandwiched between them. In flat types, a conductive polymer and a cathode body are stacked on top of an anode body.

[0029] Here, the separator holds the conductive polymer and maintains the shape of the solid electrolyte layer. The separator also prevents short-circuiting between the anode body and the cathode body. If the solid electrolyte layer maintains its shape by itself and separates the anode body and the cathode body, the separator can be omitted from the configuration of the solid electrolytic capacitor.

[0030] The conductive polymer is formed using a conductive polymer liquid. The conductive polymer liquid is a dispersion liquid in which a conductive polymer is dispersed. The solid electrolyte layer is formed by impregnating a separator with this conductive polymer liquid and drying it. Alternatively, the solid electrolyte layer is formed by applying this conductive polymer to an anode body and drying it. The solid electrolyte layer is in close contact with the anode body and functions as a true cathode.

[0031] An anode lead is connected to the anode body, and a cathode lead is connected to the cathode body. The solid electrolytic capacitor is electrically connected to the mounted circuit via these anode and cathode leads. By being connected to the mounted circuit, the solid electrolytic capacitor becomes a passive element that obtains capacitance through the dielectric polarization of the dielectric oxide film and stores and discharges electric charge.

[0032] (Anode Body) Fig. 1 is a schematic diagram showing an anode body of a solid electrolytic capacitor. As shown in Fig. 1, the anode body is a foil body having a thickness on the order of micrometers. This anode body includes, from the center in the thickness direction toward both foil surfaces, a valve metal substrate 1, a dielectric oxide film 2, and a hydrated oxide film 3. That is, the valve metal substrate 1 is located at the center in the thickness direction of the anode body. The hydrated oxide film 3 is located as the outermost layer of the anode body. The dielectric oxide film 2 is located between the valve metal substrate 1 and the hydrated oxide film 3.

[0033] The dielectric oxide film 2 is further divided into a void repair layer 21 and a void layer 22. The void repair layer 21 is a region on the valve metal substrate 1 side and is in contact with the valve metal substrate 1. The void layer 22 is a region away from the valve metal substrate 1, in other words, on the surface side of the dielectric oxide film 2. An unrepaired layer 23 may be interposed between the void repair layer 21 and the void layer 22. Alternatively, the entire region of the unrepaired layer 23 may be replaced by the void repair layer 21, and the void repair layer 21 and the void layer 22 may be in contact with each other.

[0034] The valve metal substrate 1 is a core layer in which the base metal remains as unoxidized valve metal. In the wound type, the valve metal substrate 1 is in the form of a long strip obtained by stretching the valve metal, while in the laminated type, the valve metal substrate 1 is in the form of a flat plate or a sintered body obtained by molding and sintering powder into a flat plate. Valve metals include aluminum, tantalum, niobium, niobium oxide, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. The purity of the anode body is preferably 99.9% or higher, but impurities such as silicon, iron, copper, magnesium, and zinc may be contained.

[0035] The hydrated oxide film 3 is a layer of needle-like structures containing hydrated oxide of aluminum. ２ O or Al ２ O ３ ・xH ２ The hydrated oxide film 3 has a dense interior and functions as a resistive layer to improve the withstand voltage of the solid electrolytic capacitor. However, the hydrated oxide film 3 may be entirely replaced by the dielectric oxide film 2 and disappear during the manufacturing process of the solid electrolytic capacitor, or the step of forming the hydrated oxide film 3 may be omitted altogether.

[0036] This hydrated oxide film 3 is formed by hot water treatment of the valve metal substrate 1. In the hot water treatment, the valve metal substrate 1 is immersed in pure water at 80°C or higher or boiling. This hot water treatment replaces the valve metal substrate 1 with the hydrated oxide film 3 from the surface toward the depth. The immersion time may be determined based on the desired thickness of the hydrated oxide film 3 and the balance between withstand voltage and capacitance.

[0037] The dielectric oxide film 2 is an aluminum oxide layer containing γ-alumina, a crystalline oxide. The first chemical conversion treatment replaces the hydrated oxide film 3 with the dielectric oxide film 2 from the interface between the valve metal substrate 1 and the hydrated oxide film 3 toward the surface of the hydrated oxide film 3. That is, the hydrated oxide is converted to γ-alumina from the interface between the valve metal substrate 1 and the hydrated oxide film 3. The entire hydrated oxide film 3 may be replaced with the dielectric oxide film 2.

[0038] In the first chemical conversion treatment, a voltage corresponding to a desired withstand voltage is applied to the anode body on which the hydrated oxide coating 3 is formed in a chemical conversion solution that does not contain halogen ions. The chemical conversion solution may be 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 aqueous solution such as ammonium adipate.

[0039] The void layer 22 has a large number of uniformly distributed microvoids within the layer that cannot be penetrated by conductive polymer particles having an average particle size. In other words, the void layer 22 is a region of the dielectric oxide film 2 that has a large number of microvoids whose diameter is smaller than the average particle size of the conductive polymer particles.

[0040] Generally, in electrolytic capacitors using an electrolyte, voids in the dielectric oxide film 2 reduce the withstand voltage. Therefore, in electrolytic capacitors using an electrolyte, reducing the voids through depolarization improves the withstand voltage. However, in solid electrolytic capacitors, reducing the voids generated by the first chemical conversion treatment through depolarization does not have much effect on improving the withstand voltage. However, by actively introducing a void layer 22 containing numerous microvoids into the dielectric oxide film 2, which does not allow the conductive polymer to enter, the withstand voltage of the solid electrolytic capacitor can be improved.

[0041] Although this is speculation and not intended to be limiting, the conductive component in a solid electrolytic capacitor is a conductive polymer, which does not easily penetrate into the microvoids. At the very least, the concentration of the conductive polymer in the void layer 22 is lower than the concentration of the conductive polymer in the solid electrolyte layer.

[0042] However, the liquid component of the conductive polymer liquid penetrates into the microvoids, and some of it remains even after the drying process. The liquid component of the conductive polymer liquid acts to repair defects in the dielectric oxide film 2. That is, the void layer 22 has microvoids, and while excluding the conductive polymer, the liquid component of the conductive polymer liquid, which acts to repair defects in the dielectric oxide film 2, is filled in. This reduces the risk of dielectric breakdown in the solid electrolytic capacitor and improves the withstand voltage.

[0043] The hydrated oxide film 3 also has a dense interior, which prevents the intrusion of conductive polymers. If the hydrated oxide film 3 is present, a conductive polymer exclusion layer is formed with a thickness equal to the combined thickness of the void layer 22 and the hydrated oxide film 3. This further improves the withstand voltage of the solid electrolytic capacitor.

[0044] The void layer 22 is formed by performing a void introduction treatment after the first chemical conversion treatment. The void introduction treatment increases the number of microvoids in the dielectric oxide film 2. That is, the void introduction treatment forms the void layer 22 in which the number of microvoids is increased in the dielectric oxide film 2.

[0045] In the void introduction treatment, the anode body having the dielectric oxide film 2 formed thereon is immersed in a void treatment liquid consisting of one or more of an acidic solution, an alkaline solution, and pure water. Examples of the acidic solution, alkaline solution, or pure water include a phosphoric acid solution, a sulfuric acid solution, a nitric acid solution, a sodium hydroxide solution, a potassium hydroxide solution, an ammonia solution, and pure water at 60° C. or higher. Immersion in the acidic solution, alkaline solution, or pure water stretches the dielectric oxide film 2, expands the gas in the dielectric oxide film 2, or chemically dissolves the dielectric oxide film 2, thereby generating new microvoids or enlarging existing coarse voids.

[0046] Here, in the first chemical conversion treatment aimed at achieving a high withstand voltage, when the hydrated oxide film 3 is converted into the dielectric oxide film 2, shrinkage occurs due to a decrease in specific volume, and coarse voids are formed in the dielectric oxide film 2. The coarse voids are distributed in a range of approximately 50 nm to 100 nm in equivalent circle diameter, and conductive polymers of average particle size can enter them. In the void introduction treatment, a large number of microvoids are formed, and open paths made up of a series of microvoids open to the coarse voids. These open paths provide a clue for repairing the coarse voids.

[0047] In the void introduction treatment, a void layer 22 is formed from the interface with the void treatment solution toward the depth of the anode body. In the void introduction treatment, the surface region of the dielectric oxide film 2 is converted into the void layer 22. The thickness of the void layer 22 is determined by the immersion time in the treatment solution and the temperature of the treatment solution.

[0048] The void repair layer 21 is a region of the dielectric oxide film 2 where the voids have been repaired and eliminated by the second chemical conversion treatment after the void introduction treatment has created open paths made up of a series of microvoids. The void repair layer 21 is formed by repairing the dielectric oxide film 2 in sequence from the interface between the valve metal substrate 1 and the dielectric oxide film 2 toward the surface of the dielectric oxide film 2 by the second chemical conversion treatment, thereby filling the coarse voids and microvoids. That is, the void repair layer 21 extends from the interface with the valve metal substrate 1, and is a layer in which the coarse voids and microvoids have either disappeared or are fewer than those in the void layer 22 and the unrepaired layer 23.

[0049] In the second chemical conversion treatment, a predetermined voltage is applied to the anode body with the void layer 22 formed in a chemical conversion solution that does not contain halogen ions. The chemical conversion solution may be a phosphoric acid-based chemical conversion solution such as ammonium dihydrogen phosphate, a boric acid-based chemical conversion solution such as ammonium borate, an adipic acid-based aqueous solution such as ammonium adipate, or a dispersion medium and additives for a conductive polymer solution. In the second chemical conversion treatment, the chemical conversion solution reaches the coarse voids through the open paths formed by the microvoids. Therefore, in the second chemical conversion treatment, the coarse voids and the microvoids are repaired and disappear.

[0050] The applied voltage of the second chemical conversion treatment is set lower than that of the first chemical conversion treatment. This second chemical conversion treatment generates a void repair layer 21 that is free of coarse voids and has no or few microvoids, while leaving behind a void layer 22. In other words, the applied voltage of the second chemical conversion treatment is set to a level at which, at most, the void repair layer 21 reaches the void layer 22, or the void layer 22 does not disappear completely.

[0051] This void repair layer 21 reduces leakage current in the solid electrolytic capacitor. While this is speculation and not intended to be limiting, if liquid components such as the dispersion medium and liquid additives of the conductive polymer liquid penetrate into the voids, the liquid components of the conductive polymer liquid form a conductive path, increasing the leakage current of the solid electrolytic capacitor. However, the void repair layer 21 has few or no microvoids, let alone large voids. Therefore, the liquid components of the conductive polymer liquid are unlikely to penetrate the void repair layer 21. The conductive path formed by the liquid components of the conductive polymer liquid is interrupted by the void repair layer 21. Therefore, even if a void layer 22 containing microvoids is present, the void repair layer 21 can suppress leakage current in the solid electrolytic capacitor.

[0052] In this way, the dielectric oxide film 2 is formed by the void repair layer 21 and the void layer 22, and the solid electrolytic capacitor has a high withstand voltage and suppresses leakage current of the solid electrolytic capacitor. The withstand voltage and leakage current are adjusted by the respective thicknesses of the void repair layer 21 and the void layer 22. Furthermore, the respective thicknesses of the void repair layer 21 and the void layer 22 are adjusted by the predetermined applied voltage in the second chemical conversion treatment.

[0053] Furthermore, from the viewpoint of further improving the withstand voltage of the solid electrolytic capacitor, the applied voltage of the second chemical conversion treatment to form the void repair layer 21 is preferably lower than the applied voltage of the first chemical conversion treatment and is set to 400 V or less. In other words, the withstand voltage of the void repair layer 21 is preferably set to 400 V or less. If a void repair layer 21 with a thickness of 0.9 to 1.5 nm is required to obtain a withstand voltage of 1 V, it is preferable to form the void repair layer 21 with a thickness of 360 nm or more or 600 nm or less.

[0054] The preferred range of 400 V or less for the applied voltage in the second chemical conversion treatment is applicable when polyethylene dioxythiophene doped with polystyrene sulfonic acid (PEDOT:PSS) is used as the conductive polymer. When polyethylene dioxythiophene doped with polystyrene sulfonic acid (PEDOT:PSS) is used as the conductive polymer, the withstand voltage of the solid electrolytic capacitor is further improved in relation to the void repair layer 21.

[0055] The mechanism of the improvement in voltage resistance associated with the void repair layer 21 is speculated, but is not limited to this, and is speculated as follows: Namely, charges of the conductive polymer may be distributed stochastically on the surface of the void repair layer 21. If the charges distributed on the surface of the void repair layer 21 are injected into a weak part of the void repair layer 21, the resistance of the weak part decreases. Charges accumulate on the surface of the void repair layer 21, and if the resistance of the weak part into which the charges are injected decreases, the charges accumulated on the surface of the void repair layer 21 will concentrate in the weak part, causing dielectric breakdown of the void repair layer 21.

[0056] However, in relation to the probability of the distribution of charges in the conductive polymer on the surface of the void repair layer 21, if the resistance of the void repair layer 21 is uniformly low, even if the charges in the conductive polymer are distributed on the surface of the void repair layer 21, the charges will not accumulate, and the current will flow uniformly and disperse within the void repair layer 21, preventing charges from accumulating on the surface of the void repair layer 21. Therefore, dielectric breakdown due to charge concentration in the weak parts of the void repair layer 21 will not occur. Furthermore, in relation to polystyrene sulfonic acid-doped polyethylenedioxythiophene (PEDOT:PSS), if the withstand voltage of the void repair layer 21 is set to 400 V or less, dielectric breakdown of the void repair layer 21 will not occur, and the withstand voltage of the solid electrolytic capacitor will be further improved.

[0057] Even if the withstand voltage of the void repair layer 21 is set to 400 V or less, the leakage current can be suppressed by the presence of the void repair layer 21. Therefore, the applied voltage in the second chemical conversion treatment may be determined according to the target leakage current and withstand voltage.

[0058] Furthermore, even if the second chemical conversion treatment does not cause the void repair layer 21 to reach the void layer 22, the presence of the void repair layer 21 reduces the leakage current of the solid electrolytic capacitor. Therefore, the predetermined applied voltage of the second chemical conversion treatment may be set even lower to provide an unrepaired layer 23 between the void repair layer 21 and the void layer 22. In other words, the unrepaired layer 23 is a layer in which large voids and microvoids have not been repaired by the second chemical conversion treatment, and more voids remain in the unrepaired layer 23 than in the void repair layer 21.

[0059] The liquid component of the conductive polymer solution permeates the unrepaired layer 23 via the void layer 22, and together with the void layer 22, the unrepaired layer 23 serves as a layer that stores the liquid component that has the effect of repairing defects in the dielectric oxide film 2. Furthermore, due to the void layer 22 located on the surface, or due to both the hydrated oxide film 3 and the void layer 22, there is little or no conductive polymer in the unrepaired layer 23. Therefore, the unrepaired layer 23, together with the void layer 22, also improves the withstand voltage of the solid electrolytic capacitor.

[0060] The remaining hydrated oxide film 3 after the replacement with the dielectric oxide film 2 may be subjected to an acid treatment to adjust its thickness or may be completely removed. Specifically, the anode foil is immersed in phosphoric acid or the like for a short period of time to perform the acid treatment, dissolving the hydrated oxide film 3 from the surface, and a series of steps is repeated to perform the repair chemical conversion treatment. In the repair chemical conversion treatment, the anode body is immersed in a chemical conversion solution and a voltage is applied. The chemical conversion solution may be a phosphoric acid-based chemical conversion solution such as ammonium dihydrogen phosphate, a boric acid-based chemical conversion solution such as ammonium borate, an adipic acid-based chemical conversion solution such as ammonium adipate, or an aqueous solution of a mixture of boric acid and a dicarboxylic acid such as citric acid.

[0061] A surface-expanding layer is formed on one or both sides of the anode body. The surface-expanding layer is a surface layer that has been treated to increase its surface area beyond its projected area. It can be an etching layer formed by etching the foil, a sintered layer formed by adhering and sintering valve metal powder to the foil, or a vapor-deposited layer formed by vapor-depositing valve metal particles onto the foil. That is, the surface-expanding layer has a porous structure consisting of tunnel-like pits, spongy pits, or voids between densely packed powder or particles. The dielectric oxide film 2 and the hydrated oxide film 3 are formed along the irregularities of this surface-expanding layer.

[0062] The tunnel-shaped etching pit is a hole dug in the thickness direction of the anode body and may penetrate the anode body. This tunnel-shaped etching pit is typically formed by passing a direct current in an acidic aqueous solution containing halogen ions, such as hydrochloric acid. The tunnel-shaped etching pit is further expanded by passing a direct current in an acidic aqueous solution, such as nitric acid. The spongy etching pit is a sponge-like expanded surface layer in which fine voids are connected and expanded in a spatial manner. This spongy etching pit is formed by passing an alternating current in an acidic aqueous solution containing halogen ions, such as hydrochloric acid.

[0063] The sintered layer is produced by attaching a powder of a valve action metal, which is the same or different from the foil, to the foil and sintering it. The powder can be obtained by a milling method, atomization method, melt spinning method, rotating disk method, rotating electrode method, etc. The powder is made into a paste using a binder or solvent, applied to the foil, and dried. The powder is then sintered by heating in a vacuum or reducing atmosphere, etc. The atomization method may be water atomization, gas atomization, or water gas atomization. The vapor deposition layer is produced by, for example, a resistance heating vapor deposition method or an electron beam heating vapor deposition method. This vapor deposition layer is formed by heating and evaporating a valve action metal, which is the same or different from the foil, using resistance heat or electron beam energy, and depositing the vapor of the valve action metal particles on the surface of the foil.

[0064] 2 is a flowchart showing the anode processing steps for such an anode body. First, a surface-expanding step is performed in which a porous surface-expanding layer is formed on one or both sides of the foil (step S01). To increase the breakdown voltage of the solid electrolytic capacitor, it is preferable to form tunnel-shaped etching pits in the surface-expanding step.

[0065] After the surface-expanding step, a hot water treatment step is carried out to form a hydrated oxide film 3 on the surface of the valve metal substrate 1 along the irregularities of the surface-expanding layer (step S02). The hot water treatment step of forming the hydrated oxide film 3 may be omitted.

[0066] After the hot water treatment step, a first chemical conversion treatment step is performed in which the hydrated oxide film 3 is transformed into the dielectric oxide film 2 from the interface between the valve metal substrate 1 and the hydrated oxide film 3 toward the outer surface of the hydrated oxide film 3 (step S03). In the first chemical conversion treatment step, the hydrated oxide film 3 may be completely removed.

[0067] After the first chemical conversion treatment, a void introduction treatment is performed to increase the number of voids in the dielectric oxide film 2 (step S04). The void introduction treatment introduces microvoids into the dielectric oxide film 2 to form a void layer 22, and also opens up large voids that were generated in the first chemical conversion treatment.

[0068] After the void introduction treatment, a second chemical conversion treatment step is performed (step S05), in which coarse voids and microvoids at the interface with the valve metal substrate 1 are repaired and replaced with a void repair layer 21. In the second chemical conversion treatment step, an applied voltage is set that is lower than the applied voltage in the first chemical conversion treatment but leaves a void layer 22. The applied voltage at which the void layer 22 remains is approximately less than 90% of the applied voltage in the first chemical conversion treatment. When PEDOT:PSS is used as the conductive polymer, a voltage of 400 V or less is preferably applied in the second chemical conversion treatment step. Thereafter, if necessary, a series of steps, including dissolution treatment of the hydrated oxide film 3 and repair chemical conversion treatment, may be repeated to adjust the thickness of the hydrated oxide film 3, including to zero.

[0069] The void repair layer 21 can also be formed by performing the second chemical conversion treatment during the aging treatment of the solid electrolytic capacitor. Fig. 3 is a flowchart showing a manufacturing method for forming the void repair layer 21 by the aging treatment.

[0070] As shown in FIG. 3, after the surface enlargement process (step S01), the hot water treatment process (step S02), the first chemical conversion treatment process (step S03), and the void introduction process (step S04), an element formation process for assembling a capacitor element is performed (step S05).

[0071] In the element formation process, the anode body and cathode body that have been subjected to void introduction treatment, or these are combined with a separator. In the solid electrolyte layer formation process, the assembly of the anode body, cathode body, and separator is impregnated with a conductive polymer liquid and dried. Alternatively, in the solid electrolyte layer formation process, the conductive polymer liquid is applied to the anode body and dried, and the cathode body is laminated on the solid electrolyte layer.

[0072] After this element formation process, a second chemical conversion treatment is performed (step S05). This second chemical conversion treatment is an aging treatment in which a voltage lower than that of the first chemical conversion treatment is applied to the solid electrolytic capacitor. During the aging treatment, the void repair layer 21 expands from the interface between the valve metal substrate 1 and the dielectric oxide film 2. The applied voltage in this aging treatment is also set lower than that of the first chemical conversion treatment, but at a level that does not cause the void layer 22 to disappear.

[0073] Preferably, the void repair layer 21 is formed by a second chemical conversion treatment before the element formation process. When the void repair layer 21 is formed by the second chemical conversion treatment before the element formation process, the capacitance of the solid electrolytic capacitor becomes higher than when the void repair layer 21 is formed by an aging treatment.

[0074] (Cathode body) The cathode body is a cathode foil that is drawn using a valve metal as the material. The purity of the cathode foil is preferably 99% or more. Like the anode body, the cathode foil has a surface expansion layer formed. Plain foil without a surface expansion layer may also be used as the cathode foil. The cathode foil may have a natural oxide film or a thin oxide film (about 1 to 10 V) formed by chemical conversion treatment. The natural oxide film is formed when the cathode foil reacts with oxygen in the air.

[0075] A conductive layer may be added to the outermost surface of the cathode foil. The conductive layer may be formed, for example, by vapor deposition and contain a metal nitride, metal carbide, or metal carbonitride, or may be a carbon layer applied by slurry casting, doctor blade coating, spraying, or the like. The carbon layer may contain a carbon material, such as fibrous carbon, carbon powder, or a mixture thereof. Examples of fibrous carbon include carbon nanotubes and carbon nanofibers. Examples of carbon powder include activated carbon derived from natural plant tissues such as coconut husks, synthetic resins such as phenols, fossil fuels such as coal, coke, and pitch, carbon blacks such as ketjen black, acetylene black, and channel black, carbon nanohorns, amorphous carbon, natural graphite, artificial graphite, graphitized ketjen black, and mesoporous carbon.

[0076] Alternatively, the cathode body is a laminate of a metal layer and a carbon layer, with the carbon layer facing the anode body. The carbon layer is formed by forming a solid electrolyte layer on the anode body, applying a paste to the solid electrolyte layer, and then curing the paste by heating. The metal layer is, for example, a silver layer, and is formed by applying a paste to the carbon layer and then curing the paste by heating.

[0077] (Solid Electrolyte Layer) The conductive polymer of the solid electrolyte layer is a conjugated polymer that is either a self-doped type doped with intramolecular dopant molecules or an externally doped type doped with external dopant molecules. Conjugated polymers are obtained by chemical oxidative polymerization or electrolytic oxidative polymerization of monomers or their derivatives having π-conjugated double bonds. Doped conjugated polymers exhibit high conductivity. That is, conductivity is exhibited by adding a small amount of a dopant, such as an acceptor that easily accepts electrons or a donor that easily donates electrons, to a conjugated polymer.

[0078] 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.

[0079] 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. The thiophene derivative is preferably a compound selected from thiophenes having substituents at the 3rd and 4th positions, and the substituents at the 3rd and 4th positions of the thiophene ring may form a ring together with the carbon atoms at the 3rd and 4th positions. The alkyl group or alkoxy group preferably has 1 to 16 carbon atoms.

[0080] In particular, a polymer of 3,4-ethylenedioxythiophene, known as EDOT, i.e., poly(3,4-ethylenedioxythiophene), known as PEDOT, is particularly preferred. Furthermore, a substituent may be added to 3,4-ethylenedioxythiophene. For example, an alkylated ethylenedioxythiophene having an alkyl group having 1 to 5 carbon atoms added as a substituent may be used. Examples of alkylated ethylenedioxythiophenes include methylated ethylenedioxythiophene (i.e., 2-methyl-2,3-dihydrothieno[3,4-b][1,4]dioxin), ethylated ethylenedioxythiophene (i.e., 2-ethyl-2,3-dihydrothieno[3,4-b][1,4]dioxin), butylated ethylenedioxythiophene (i.e., 2-butyl-2,3-dihydrothieno[3,4-b][1,4]dioxin), and 2-alkyl-3,4-ethylenedioxythiophene.

[0081] 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. Furthermore, a polymer or a monomer may be used. Examples of dopants include inorganic acids such as polyanions, boric acid, nitric acid, and phosphoric acid, and organic acids such as acetic acid, oxalic acid, citric acid, tartaric acid, squaric acid, rhodizonic acid, croconic acid, salicylic acid, p-toluenesulfonic acid, 1,2-dihydroxy-3,5-benzenedisulfonic acid, methanesulfonic acid, trifluoromethanesulfonic acid, borodisalicylic acid, bisoxalateborate acid, sulfonylimide acid, dodecylbenzenesulfonic acid, propylnaphthalenesulfonic acid, and butylnaphthalenesulfonic acid.

[0082] Examples of the polyanion include a substituted or unsubstituted polyalkylene, a substituted or unsubstituted polyalkenylene, a substituted or unsubstituted polyimide, a substituted or unsubstituted polyamide, and a substituted or unsubstituted polyester, and include a polymer consisting only of a structural unit having an anionic group, and a polymer consisting of a structural unit having an anionic group and a structural unit not having an anionic group. Specific examples of the polyanion include polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallyl sulfonic acid, polyacryl sulfonic acid, polymethacrylic acid, poly(2-acrylamido-2-methylpropane sulfonic acid), polyisoprene sulfonic acid, polyacrylic acid, polymethacrylic acid, and polymaleic acid.

[0083] The interfacial characteristics of the void repair layer 21 differ depending on the type of conductive polymer, and the probability and amount of charge transferred from the conductive polymer differ, so the voltage at which the void repair layer 21 breaks down also differs. Therefore, when a conductive polymer other than PEDOT:PSS is selected, the withstand voltage of the solid electrolytic capacitor can be further increased by changing the applied voltage of the second chemical conversion treatment depending on the selected conductive polymer.

[0084] Various additives may be added to solid electrolytic capacitors. For example, the conductive polymer solution used to form the solid electrolyte layer may contain additives such as polyhydric alcohols, such as ethylene glycol and glycerin. Polyhydric alcohols have high boiling points and tend to remain in the solid electrolyte layer after the conductive polymer solution is impregnated and dried. The polyhydric alcohols cause changes in the higher-order structure of the conductive polymer and reorientation of the crystalline structure of the polymer chains, thereby reducing the ESR of the solid electrolytic capacitor and further improving its withstand voltage. Furthermore, the conductive polymer solution may contain sugar alcohols, such as sorbitol. The sugar alcohols improve the chemical conversion properties of the dielectric oxide film and further increase the withstand voltage of the solid electrolytic capacitor.

[0085] The conductive polymer liquid may also contain conventional additives such as an organic binder, a surfactant, a dispersant, an antifoaming agent, a coupling agent, an antioxidant, and an ultraviolet absorber. The pH of the conductive polymer liquid is preferably 2 to 9. If the pH is in the range of 2 to 9, dissolution of the separator, anode body, and cathode body is suppressed.

[0086] The solvent for this conductive polymer solution is not particularly limited. The solvent for the conductive polymer solution is typically water, an organic solvent, or a mixture of an organic solvent and water. Examples of organic solvents include polar solvents, alcohols, esters, hydrocarbons, carbonate compounds, ether compounds, chain ethers, heterocyclic compounds, and nitrile compounds. The void repair layer 21 prevents the penetration of additives such as polyhydric alcohols in addition to these solvents, thereby suppressing leakage current.

[0087] Examples of polar solvents include N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide. Examples of alcohols include methanol, ethanol, propanol, and butanol. Examples of esters include ethyl acetate, propyl acetate, and butyl acetate. Examples of hydrocarbons include hexane, heptane, benzene, toluene, and xylene. Examples of carbonate compounds include ethylene carbonate and propylene carbonate. Examples of ether compounds include dioxane and diethyl ether. Examples of linear ethers include ethylene glycol dialkyl ether, propylene glycol dialkyl ether, polyethylene glycol dialkyl ether, and polypropylene glycol dialkyl ether. Examples of heterocyclic compounds include 3-methyl-2-oxazolidinone. Examples of nitrile compounds include acetonitrile, glutarodinitrile, methoxyacetonitrile, propionitrile, and benzonitrile.

[0088] In order to promote the impregnation of the conductive polymer liquid, a decompression treatment or a pressurization treatment may be performed as necessary. The impregnation process may be repeated multiple times. After the capacitor element is impregnated with the conductive polymer liquid, a drying process is performed to remove the portion that has penetrated into the void layer 22 and to remove the liquid component of the conductive polymer liquid.

[0089] (Separator) Examples of separators include cellulose papers such as kraft, Manila hemp, esparto, hemp, and rayon, and mixtures 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. These resins can be used alone or in combination.

[0090] However, the separator separates the anode body and the cathode body to prevent short circuits and also holds the conductive polymer in place. If the conductive polymer can maintain its shape by itself and can separate the anode body and the cathode body, the separator can be omitted.

[0091] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0092] (Examples 1 and 2) (Anode Body) The anode bodies of Examples 1 and 2 and Comparative Examples 1 to 3 were fabricated as follows: First, an aluminum foil having a foil thickness of 120 μm and a purity of 99.99% was used as the anode body.

[0093] The aluminum foil was immersed in distilled water at 95°C for 10 minutes in a hot water treatment, thereby forming a hydrated oxide film 3 on the surface layer of the aluminum foil. Then, in a first chemical conversion treatment, the hydrated oxide film 3 was dehydrated and converted into a dielectric oxide film 2, which is aluminum oxide with high crystallinity, while leaving the surface layer of the hydrated oxide film 3. In the first chemical conversion treatment, after the hydrated oxide film 3 was formed, the aluminum foil was immersed in a solution of boric acid (H O ) at a concentration of 0.5 mol / L at a liquid temperature of 90°C. ３ BO ３ ) aqueous solution and 50 mA / cm ２ A voltage was applied while flowing a constant current of 1000 V. The voltage was applied until the chemical conversion voltage reached 700 V. The anode body of Comparative Example 1 was completed by the above-described hot water treatment and first chemical conversion treatment.

[0094] The other examples and comparative examples then proceeded to a void introduction treatment. In the void introduction treatment, the anode body on which the dielectric oxide film 2 was formed was immersed in pure water at a liquid temperature of 95°C for 600 seconds. As a result, a void layer 22 was formed in the dielectric oxide film 2. The anode body of comparative example 2 was completed by the above-described hot water treatment, first chemical conversion treatment, and void introduction treatment.

[0095] The other examples and comparative examples then went on to the second chemical conversion treatment. In the second chemical conversion treatment, a void repair layer 21 was formed on the dielectric oxide film 2. In this second chemical conversion treatment, a solution of boric acid (H ３ BO ３ ) aqueous solution and 50 mA / cm２ A voltage was applied while flowing a constant current of 100 V. In Example 1, the chemical conversion voltage was applied until it reached 200 V, which is lower than the 700 V of the first chemical conversion treatment. In Example 2, the chemical conversion voltage was applied until it reached 400 V, which is lower than the 700 V of the first chemical conversion treatment. In Comparative Example 3, the chemical conversion voltage was applied until it reached 630 V, which is lower than the 700 V of the first chemical conversion treatment.

[0096] (Structural Observation of Anode Body) The cross sections of the anode bodies of Comparative Examples 1 and 2 were observed at 30k magnification using a scanning transmission electron microscope. The cross sections of the anode bodies of Examples 1 and 2 and Comparative Example 3 were observed at 30k magnification using a scanning electron microscope. In FIG. 4, (a) is a photograph showing a cross-sectional STEM image of Comparative Example 1, (b) is a photograph showing a cross-sectional SEM image of Comparative Example 2, FIG. 5 is a photograph showing a cross-sectional SEM image of Example 1, FIG. 6 is a photograph showing a cross-sectional SEM image of Example 2, and FIG. 7 is a photograph showing a cross-sectional SEM image of Comparative Example 3.

[0097] 4(a), in the anode body of Comparative Example 1, a hydrated oxide film 3 is formed on the surface layer of a valve metal substrate 1 by the hot water treatment step, and a dielectric oxide film 2 is formed by the first chemical conversion treatment, leaving the surface layer of the hydrated oxide film 3. In particular, it can be seen that there are many conspicuously large voids in the dielectric oxide film 2 on the valve metal substrate 1 side.

[0098] Next, as shown in Fig. 4(b), it can be seen that the anode body of Comparative Example 2 has a void introduction step added thereto compared to Comparative Example 1, and thus a void layer 22 is formed in the surface layer of the dielectric oxide film 2. In Fig. 4(b), the void layer 22 has countless microvoids generated in the surface layer of the dielectric oxide film 2, and is striped compared to the underlying layer.

[0099] As shown in Figure 5, the anode body of Example 1 was subjected to a second chemical conversion treatment in addition to that of Comparative Example 2, and as a result, a void repair layer 21 was formed below the dielectric oxide film 2, along with a void layer 22. In the second chemical conversion treatment performed in Example 1, 200 V was applied, compared to the 700 V applied in the first chemical conversion treatment. As a result, an unrepaired layer 23 remains between the void layer 22 and the void repair layer 21. In the unrepaired layer 23, voids are noticeable at the boundary with the void repair layer 21. However, compared to this boundary where the voids are noticeable, the void repair layer 21 appears smooth, and it can be seen that both large and small voids have disappeared.

[0100] 6 , the anode body of Example 2 is subjected to an additional second chemical conversion treatment compared to Comparative Example 2, and as a result, a void repair layer 21 is formed on the dielectric oxide film 2 together with a void layer 22. In the second chemical conversion treatment performed in Example 2, 400 V is applied, whereas in the first chemical conversion treatment, 700 V is applied. Therefore, as can be seen from a comparison with Example 1, in Example 2, the void repair layer 21 extends to the boundary of the void layer 22.

[0101] 7 , the anode body of Comparative Example 3 further includes a second chemical conversion treatment in comparison with Comparative Example 1, and therefore a void repair layer 21 is formed in the dielectric oxide film 2. However, in the second chemical conversion treatment carried out in Comparative Example 3, 630 V is applied, whereas in the first chemical conversion treatment, 700 V is applied. Therefore, as can be seen from a comparison with Example 2, in Comparative Example 3, the void repair layer 21 extends over the entire area of ​​the void layer 22, and the void layer 22 has disappeared.

[0102] (Solid Electrolytic Capacitor) After the anode body processing process, the process proceeded to the element formation process for the solid electrolytic capacitor. In the element formation process, a conductive polymer solution was first dripped onto the anode bodies of Examples 1 and 2 and Comparative Examples 1 to 3. The conductive polymer solution was a dispersion in which a conductive polymer was dispersed in water. The conductive polymer was polyethylene dioxythiophene (PEDOT:PSS) doped with polystyrene sulfonic acid. The conductive polymer was dispersed in the conductive polymer solution at a ratio of 1.0 wt %. The conductive polymer solution was adjusted to pH 4 with ammonia water and contained 10 vol % ethylene glycol and 85 wt % sorbitol relative to the conductive polymer. The conductive polymer solution was dispersed using ultrasound.

[0103] The anode body has a projected area of ​​0.785 cm ２ After the conductive polymer solution was dropped, the anode body was allowed to stand for 10 minutes in a temperature environment of 60°C, and then allowed to stand for 30 minutes in a temperature environment of 110°C. This dried the anode body, and a solid electrolyte layer of conductive polymer was formed on the anode body.

[0104] After forming the solid electrolyte layer, carbon paste was applied onto the solid electrolyte layer and allowed to harden by being left in a temperature environment of 110°C for 30 minutes. Furthermore, silver paste was applied onto the carbon layer, and at the same time, copper foil was adhered as a lead terminal. The silver paste was allowed to harden by being left in a temperature environment of 110°C for 30 minutes with copper foil adhered to the silver paste portion before hardening. The carbon layer, silver layer, and copper foil layer described above correspond to the cathode body of the solid electrolytic capacitor.

[0105] (Measurement of the amount of penetration of liquid component of conductive polymer solution) After forming the solid electrolyte layer, the element ratio of sulfur was measured by energy dispersive X-ray analysis of the cross section of the anode body of Example 2. The cross section of the anode body is a surface cut along the thickness direction of the aluminum foil.

[0106] 8 is a diagram showing the elemental ratio of sulfur at each depth in the anode body of Example 2. As shown in FIG. 8, the elemental ratio of sulfur was 0.61% in the surface layer of the void layer 22, and 0.35% in the layer below the void layer 22. In contrast, the elemental ratio of sulfur in the outermost layer of the void repair layer 21 was 0.13%, which is about one-third of the lower layer of the void layer 22, and the elemental ratio of sulfur in the layer below the outermost layer remained at 0.01% to 0.06%. In the figure, ND stands for Not Detected, indicating that measurement was not possible.

[0107] Here, the sulfur originates from the conductive polymer or polystyrene sulfonic acid that was not doped into the conductive polymer, and is contained in the liquid component of the conductive polymer liquid. Therefore, the results in Figure 8 show that the liquid component of the conductive polymer liquid has penetrated into the microvoids in the void layer 22. On the other hand, the results in Figure 8 also show that the void repair layer 21 has become a layer into which the liquid component of the conductive polymer liquid cannot penetrate due to the reduction in coarse voids and microvoids.

[0108] (Measurement of Withstand Voltage and Leakage Current) The withstand voltage and leakage current of the solid electrolytic capacitors of Examples 1 and 2 and Comparative Examples 1 to 3 were measured. The method for measuring the withstand voltage and leakage current was as follows. That is, to measure the withstand voltage and leakage current, a voltage was applied to the solid electrolytic capacitor. The starting voltage was 0 V, and the applied voltage was increased by 1 V every second. Then, while measuring the leakage current flowing through the solid electrolytic capacitor, the voltage at which the leakage current first reached 10 mA on the voltage rise curve was taken as the withstand voltage. Four solid electrolytic capacitors were produced, and the average withstand voltage of the four capacitors was calculated.

[0109] The results of the withstand voltage and leakage current are shown in Figures 9 to 12. Figure 9 (a) is a graph showing the relationship between applied voltage and leakage current in Comparative Example 1, and (b) is a graph showing the relationship between applied voltage and leakage current in Comparative Example 2. Figure 10 is a graph showing the relationship between applied voltage and leakage current in Example 1. Figure 11 is a graph showing the relationship between applied voltage and leakage current in Example 2. Figure 12 is a graph showing the relationship between applied voltage and leakage current in Comparative Example 3.

[0110] The anode body of Comparative Example 2 differs from the anode body of Comparative Example 1 in that a void layer 22 is formed in the dielectric oxide film 2. As shown in Figures 9(a) and 9(b), the withstand voltage of the solid electrolytic capacitor of Comparative Example 1 was 530 V, and the withstand voltage of the solid electrolytic capacitor of Comparative Example 2 was 830 V. The void layer 22 is a layer in which numerous microvoids are uniformly formed, and as shown in Figure 8, the liquid component of the conductive polymer liquid has penetrated into the void layer 22. It was confirmed that the liquid component has a repairing effect on the dielectric oxide film 2, thereby increasing the withstand voltage.

[0111] However, as shown in (a) and (b) of FIG. 9, the leakage current of the solid electrolytic capacitor of Comparative Example 1 was 10 －５ mA cm －２ On the other hand, the leakage current of the solid electrolytic capacitor of Comparative Example 2, which had an increased withstand voltage, was on the order of 10 －２ ~10 －１ mA cm －２ This can be assumed to be a side effect of the void layer 22.

[0112] In terms of leakage current, as shown in FIG. 10, the leakage current of the solid electrolytic capacitor of Example 1 is 10 －５ ~10 －４ mA cm －２ As shown in FIG. 11, the leakage current of the solid electrolytic capacitor of Example 2 was suppressed to the order of 10 －５ mA cm －２ That is, Examples 1 and 2 achieved a leakage current that was 1 / 100 to 1 / 1000 of that of Comparative Example 2.

[0113] Compared to the anode body of Comparative Example 2, the anode bodies of Examples 1 and 2 further include a void repair layer 21 in addition to the void layer 22 containing microvoids. The void repair layer 21 is a layer in which both coarse voids and microvoids have disappeared or been reduced, and the liquid component of the conductive polymer liquid cannot penetrate, as shown in Figure 8. As such, it can be confirmed that the anode bodies of Examples 1 and 2 improve the withstand voltage with the void layer 22, and that the void repair layer 21 and the void layer 22 increase the resistance and suppress leakage current.

[0114] Furthermore, as shown in Figure 12, even if the void introduction process and the second chemical treatment are performed, if the chemical treatment voltage of the second chemical treatment is increased to eliminate the void layer 22, the effect of the void layer 22 is lost, and although the solid electrolytic capacitor remains better than Comparative Example 1, the effect of improving the withstand voltage is reduced.

[0115] (Example 3) (Solid Electrolytic Capacitor) The solid electrolytic capacitor of Example 3 was fabricated as follows. Example 3 was fabricated using the same manufacturing method and conditions as Example 1 up to the element formation step, except that the second chemical conversion treatment was omitted. After the anode body processing step was completed without the second chemical conversion treatment, the element formation step was carried out. Then, after the element formation step, the solid electrolytic capacitor of Example 3 was subjected to an aging treatment as a second chemical conversion treatment. The aging treatment was carried out until the voltage applied to the solid electrolytic capacitor of Example 3 reached 400 V, which was lower than the 700 V applied in the first chemical conversion treatment.

[0116] (Structural Observation of Anode Body) The solid electrolytic capacitor of Example 3 was disassembled, and the cross section of the anode body was observed at 30k magnification using a scanning transmission electron microscope. Fig. 13 is a photograph showing a cross-sectional STEM image of Example 3. As shown in Fig. 13, it was confirmed that the anode body of Example 3 had a valve metal substrate 1, a dielectric oxide film 2, and a hydrated oxide film 3 formed thereon, and further had a void layer 22 and a void repair layer 21 formed within the dielectric oxide film 2. In other words, it was confirmed that the void repair layer 21 was formed even when the second chemical conversion treatment was performed by aging treatment after the element formation process.

[0117] (Measurement of the amount of penetration of liquid component of conductive polymer liquid) The element ratio of sulfur was measured by energy dispersive X-ray analysis of the cross section of the anode body of Example 3. The cross section of the anode body is a surface cut along the thickness direction of the aluminum foil.

[0118] Fig. 14 is a diagram showing the elemental ratio of sulfur at each depth in the anode body of Example 3. As shown in Fig. 14, the elemental ratio of sulfur was 0.48% in the surface layer of void layer 22, and the elemental ratio of sulfur was 0.21% in the lower layer of void layer 22. In contrast, the elemental ratio of sulfur in void repair layer 21 from the outermost layer to the deepest part was 0.01% to 0.03%, which was about 1 / 7 to 1 / 20 of the lower layer of void layer 22.

[0119] (Measurement of Withstand Voltage and Leakage Current) The withstand voltage and leakage current of the solid electrolytic capacitor of Example 3 were measured. The measurement method and conditions for the withstand voltage and leakage current for Example 3 were the same as those for Examples 1 and 2 and Comparative Examples 1 to 3. The results of the withstand voltage and leakage current are shown in Figure 15. Figure 15 is a graph showing the relationship between the applied voltage and leakage current for Example 3.

[0120] 15 with the graph of FIG. 9, the withstand voltage of the solid electrolytic capacitor of Example 3 is improved to 800 V. Furthermore, as can be seen by comparing the graph of FIG. 9(b), the leakage current of the solid electrolytic capacitor of Example 3 does not increase as in Comparative Example 2, and remains at 10 －５ mA cm －２ is kept to the order of .

[0121] In this way, it was confirmed that even if a second chemical conversion treatment is performed by aging treatment after the element formation process, as long as both the void layer 22 and the void repair layer 21 are present in the dielectric oxide film 2, the solid electrolytic capacitor can have both improved voltage resistance and suppressed leakage current.

[0122] Examples 4 to 15 Solid electrolytic capacitors of various examples and comparative examples were fabricated by varying the applied voltages for the first chemical conversion treatment and the second chemical conversion treatment as follows: In the solid electrolytic capacitors of Comparative Examples 4 and 5 and Examples 4 to 6, the first chemical conversion treatment was performed at an applied voltage of 500 V, and either the second chemical conversion treatment was not performed or the second chemical conversion treatment was performed at an applied voltage of 150 V to 450 V such that the applied voltage for the second chemical conversion treatment was 30%, 60%, 70%, and 90% of the applied voltage for the first chemical conversion treatment.

[0123] In the solid electrolytic capacitors of Comparative Examples 6 and 7 and Examples 7 to 9, the first chemical conversion treatment was performed at an applied voltage of 600 V, and either the second chemical conversion treatment was not performed or the second chemical conversion treatment was performed at an applied voltage of 180 V to 540 V so that the applied voltage of the second chemical conversion treatment was 30%, 60%, 70%, and 90% of the applied voltage of the first chemical conversion treatment.

[0124] In the solid electrolytic capacitors of Comparative Examples 8 and 9 and Examples 10 to 12, the first chemical conversion treatment was performed at an applied voltage of 700 V, and either the second chemical conversion treatment was not performed or the second chemical conversion treatment was performed at an applied voltage of 210 V to 630 V so that the applied voltage of the second chemical conversion treatment was 30%, 60%, 70%, and 90% of the applied voltage of the first chemical conversion treatment.

[0125] In the solid electrolytic capacitors of Comparative Examples 10 and 11 and Examples 13 to 15, the first chemical conversion treatment was performed at an applied voltage of 800 V, and either the second chemical conversion treatment was not performed or the second chemical conversion treatment was performed at an applied voltage of 240 V to 720 V so that the applied voltage of the second chemical conversion treatment was 30%, 60%, 70%, and 90% of the applied voltage of the first chemical conversion treatment.

[0126] These comparative examples 4 to 11 and examples 4 to 15 were produced using the same manufacturing method and under the same manufacturing conditions as example 1 up to the element formation process, except for the applied voltage in the first chemical conversion treatment and the applied voltage in the second chemical conversion treatment, including the fact that a void introduction process was performed.

[0127] The applied voltages for the first chemical conversion treatment and the second chemical conversion treatment for Comparative Examples 4 to 11 and Examples 4 to 15 are shown in Tables 1 to 4. As shown in Tables 1 to 4, when the solid electrolytic capacitors of Comparative Examples 4, 6, 8, and 10 were fabricated, the second chemical conversion treatment was omitted.

[0128] (Table 1)

[0129] (Table 2)

[0130] (Table 3)

[0131] (Table 4)

[0132] (Measurement of Withstand Voltage and Leakage Current) The withstand voltage and leakage current of the solid electrolytic capacitors of Comparative Examples 4 to 11 and Examples 4 to 15 were measured. The measurement method and conditions for the withstand voltage and leakage current for Comparative Examples 4 to 11 and Examples 4 to 15 were the same as those for Examples 1 and 2 and Comparative Examples 1 to 3. The results of the withstand voltage and leakage current are shown in Figures 16 to 19.

[0133] 16 is a graph showing the relationship between applied voltage and leakage current for Comparative Examples 4 and 5 and Examples 4 to 6. In the figure, C4 indicates Comparative Example 4, C5 indicates Comparative Example 5, E4 indicates Example 4, E5 indicates Example 5, and E6 indicates Example 6.

[0134] 17 is a graph showing the relationship between applied voltage and leakage current for Comparative Examples 6 and 7 and Examples 7 to 9. In the figure, C6 indicates Comparative Example 6, C7 indicates Comparative Example 7, E7 indicates Example 7, E8 indicates Example 8, and E9 indicates Example 9.

[0135] 18 is a graph showing the relationship between applied voltage and leakage current for Comparative Examples 8 and 9 and Examples 10 to 12. In the figure, C8 indicates Comparative Example 8, C9 indicates Comparative Example 9, E10 indicates Example 10, E11 indicates Example 11, and E12 indicates Example 12.

[0136] 19 is a graph showing the relationship between applied voltage and leakage current for Comparative Examples 10 and 11 and Examples 13 to 15. In the figure, C10 refers to Comparative Example 10, C11 refers to Comparative Example 11, E13 refers to Example 13, E14 refers to Example 14, and E15 refers to Example 15.

[0137] 12, Comparative Examples 5, 7, 9, and 11 in Figures 16 to 19 show that the applied voltage for the second chemical conversion treatment is 90% of the applied voltage for the first chemical conversion treatment. It can be seen that the improvement in the withstand voltage of the solid electrolytic capacitor is reduced compared to when the applied voltage for the second chemical conversion treatment is less than 90%. In other words, it can be seen that when the applied voltage for the second chemical conversion treatment is less than 90% of the applied voltage for the first chemical conversion treatment, the void layer 22 is not eliminated by the second chemical conversion treatment, and both a high withstand voltage and a low leakage current are achieved.

[0138] 16 to 19, almost all of Examples 4 to 15 exhibited values ​​close to the target withstand voltage of 500 V or achieved values ​​exceeding the withstand voltage of 500 V. In particular, all of Examples 9, 12, 14, and 15 achieved withstand voltages exceeding the applied voltage of the first chemical conversion treatment while maintaining low leakage current.

[0139] Specifically, in Examples 4 to 6, the applied voltage in the first chemical conversion treatment was 500 V, but as shown in Figure 16, the withstand voltage of the solid electrolytic capacitors of Examples 4 to 6 exceeded 600 V. In Examples 7 and 8, the applied voltage in the first chemical conversion treatment was 600 V, but as shown in Figure 17, the withstand voltage of the solid electrolytic capacitors of Examples 7 and 8 exceeded 750 V.

[0140] In Example 10, the applied voltage in the first chemical conversion treatment was 700 V, but as shown in Figure 18, the withstand voltage of the solid electrolytic capacitor of Example 10 approached 800 V. In Example 13, the applied voltage in the first chemical conversion treatment was 800 V, but as shown in Figure 18, the withstand voltage of the solid electrolytic capacitor of Example 13 exceeded 800 V.

[0141] Examples 4 to 6, 10, and 13 are all solid electrolytic capacitors manufactured by carrying out the second chemical conversion treatment at an applied voltage of 400 V or less. This shows that when the conductive polymer type is PEDOT:PSS and the applied voltage for the second chemical conversion treatment is 400 V or less, the breakdown voltage of the void repair layer 21 also increases, and the withstand voltage of the solid electrolytic capacitor is dramatically improved compared to those that have undergone the second chemical conversion treatment at an applied voltage of more than 400 V.

[0142] In addition, in Examples 1 and 2, the conductive polymer was PEDOT:PSS, the applied voltages for the second chemical conversion treatment were 200 V and 400 V, and as shown in Figures 10 and 11, it can be confirmed that the withstand voltage exceeded 700 V, which was the applied voltage for the first chemical conversion treatment.

[0143] REFERENCE SIGNS LIST 1 Valve metal substrate 2 Dielectric oxide film 21 Void repair layer 22 Void layer 23 Unrepaired layer 3 Hydrous oxide film

Claims

1. An anode body for a solid electrolytic capacitor comprising: a valve metal substrate; and a dielectric oxide film on the valve metal substrate, the dielectric oxide film having: a void layer on a surface side of the dielectric oxide film; and a void repair layer on a boundary side between the dielectric oxide film and the valve metal substrate.

2. The anode body of a solid electrolytic capacitor according to claim 1, further comprising a hydrated oxide film on a surface layer greater than said dielectric oxide film.

3. A solid electrolytic capacitor comprising an anode body, a cathode body, and a solid electrolyte layer, wherein the anode body has a valve metal substrate and a dielectric oxide film on the valve metal substrate, and the dielectric oxide film has: a void layer on a surface side of the dielectric oxide film; and a void repair layer on a boundary side between the dielectric oxide film and the valve metal substrate.

4. The solid electrolytic capacitor according to claim 3, wherein the solid electrolyte layer contains polyethylenedioxythiophene doped with polystyrenesulfonic acid, and the void repair layer has a withstand voltage of 400 V or less.

5. The solid electrolytic capacitor according to claim 3 or 4, wherein the anode body has a hydrated oxide film on a surface layer greater than the dielectric oxide film.

6. A method for manufacturing an anode body for a solid electrolytic capacitor, comprising: a first chemical conversion treatment for applying a predetermined chemical conversion voltage to a valve metal substrate; after the first chemical conversion treatment, a void introduction treatment for immersing the anode body in any one or more of an acidic solution, an alkaline solution, and pure water; and, after the void introduction treatment, a second chemical conversion treatment for applying a chemical conversion voltage lower than that of the first chemical conversion treatment.

7. A method for manufacturing an anode body for a solid electrolytic capacitor as described in claim 6, characterized in that the first chemical conversion treatment forms a dielectric oxide film on the valve metal substrate, the void introduction treatment forms a void layer on the surface side of the dielectric oxide film, and the second chemical conversion treatment forms a void repair layer of the dielectric oxide film on the boundary side of the valve metal substrate.

8. The method for producing an anode body for a solid electrolytic capacitor according to claim 6 or 7, further comprising a hot water treatment of immersing the valve metal base material in hot water prior to the first chemical conversion treatment.

9. A method for manufacturing a solid electrolytic capacitor having an anode body, a cathode body, and a solid electrolyte layer based on a valve metal, comprising: an anode body processing step of processing the anode body; and an element forming step of forming a capacitor element by incorporating the anode body, the cathode body, and the solid electrolyte layer, wherein the anode body processing step includes: a first chemical conversion treatment of applying a predetermined chemical conversion voltage to a valve metal base material; a void introduction treatment of immersing the anode body in any one or more of an acidic solution, an alkaline solution, and pure water after the first chemical conversion treatment; and a second chemical conversion treatment of applying a chemical conversion voltage lower than that of the first chemical conversion treatment after the void introduction treatment.

10. The method for producing a solid electrolytic capacitor according to claim 9, wherein the second chemical conversion treatment applies a chemical conversion voltage that is less than 90% of that applied in the first chemical conversion treatment.

11. The method for producing a solid electrolytic capacitor according to claim 9, wherein in the element formation process, the solid electrolyte layer containing polyethylenedioxythiophene doped with polystyrenesulfonic acid is incorporated into the capacitor element, and in the second chemical treatment in the anode body processing process, a chemical voltage of 400 V or less is applied.

12. The method for producing a solid electrolytic capacitor according to any one of claims 9 to 11, wherein the element forming step includes incorporating the anode body that has been subjected to the second chemical conversion treatment into the capacitor element.

13. A method for manufacturing a solid electrolytic capacitor as described in any one of claims 9 to 11, characterized in that in the element formation process, the anode body in which the first chemical conversion treatment and the void introduction treatment have been completed and the second chemical conversion treatment has not yet been performed is incorporated into the capacitor element, and the second chemical conversion treatment is performed after the solid electrolyte layer has been incorporated into the capacitor element by the element formation process.

14. A method for producing a solid electrolytic capacitor as described in any one of claims 9 to 11, wherein the anode body processing step includes a hot water treatment in which the valve metal base material is immersed in hot water before the first chemical conversion treatment.

15. A method for manufacturing a solid electrolytic capacitor as described in any one of claims 9 to 11, characterized in that the first chemical conversion treatment forms a dielectric oxide film on the valve metal substrate, the void introduction treatment forms a void layer on the surface side of the dielectric oxide film, and the second chemical conversion treatment forms a void repair layer on the dielectric oxide film on the boundary side of the valve metal substrate.

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