Solid electrolytic capacitor

Abstract

The solid electrolytic capacitor includes at least one capacitor element. The capacitor element includes: an anode foil including a porous portion in at least a surface layer; a dielectric layer covering at least a portion of the anode foil; and a solid electrolyte layer covering at least a portion of the dielectric layer. The solid electrolyte layer contains a first polymer component containing a conjugated polymer and a second polymer component containing a polymer anion. A peak unique to the first polymer component is observed in a Raman spectrum of a surface layer of the solid electrolyte layer. When the rated voltage of the solid electrolytic capacitor is Rv (V), the average thickness (T) of the dielectric layer is 2.5 * Rv (nm) or more.

Description

Technical Field

[0001] The present disclosure relates to a solid electrolytic capacitor. Background Art

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

[0003] The solid electrolyte can be formed by in-situ polymerization such as chemical polymerization or electrolytic polymerization. However, from the viewpoint of being able to easily form the solid electrolyte, the formation of the solid electrolyte mostly uses a method using a liquid dispersion containing a conjugated polymer and a dopant.

[0004] For example, Patent Document 1 proposes a method for manufacturing an electrolytic capacitor, which includes a step of impregnating a first dispersion solution containing particles of a first conductive polymer and a first solvent into an anode body having a dielectric film formed on its surface, and then impregnating a second dispersion solution containing particles of a second conductive polymer and a second solvent, wherein the pH of the first dispersion solution is closer to 7 than the pH of the second dispersion solution.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2013-58807 Summary of the Invention

[0008] One aspect of the present disclosure relates to a solid electrolytic capacitor including at least one capacitor element. The capacitor element includes: an anode foil having at least a porous portion on its surface layer; a dielectric layer covering at least a part of the anode foil; and a solid electrolyte layer covering at least a part of the dielectric layer. The solid electrolyte layer includes a first polymer component containing a conjugated polymer and a second polymer component containing a polymer anion. In the Raman spectrum of the surface layer of the solid electrolyte layer, a peak peculiar to the first polymer component is observed. When the rated voltage of the solid electrolytic capacitor is set to Rv (V), the average thickness T of the dielectric layer is 2.50×Rv (nm) or more.

[0009] It is possible to provide a solid electrolytic capacitor having high charge and discharge characteristics and high withstand voltage characteristics. Brief Description of the Drawings

[0010] Figure 1 It is a cross-sectional schematic view of a solid electrolytic capacitor according to an embodiment of the present disclosure. Detailed Embodiment

[0011] Before describing the embodiments of the present disclosure, the problems of the prior art will be briefly described. In a solid electrolytic capacitor, from the viewpoint of ensuring a high capacitance, a porous portion is formed at least on the surface layer of the anode body. If a liquid dispersion containing a conductive polymer is used, it is easy to obtain a solid electrolyte layer with a relatively large thickness, and thus it is advantageous in ensuring a high withstand voltage. However, if a liquid dispersion is used, it is difficult for the conductive polymer to fill the concave portions of the porous portion, and it is difficult to ensure a high adhesion between the anode body and the solid electrolyte layer, and a high adhesion between the inner layer formed in the concave portion and the outer layer formed on the outside of the porous portion. Therefore, when the solid electrolytic capacitor is repeatedly charged and discharged, the capacitance reduction is large, and it is difficult to obtain high charge and discharge characteristics.

[0012] In the case where the solid electrolyte layer is formed by electrolytic polymerization, it is easy to fill into the concave portions of the porous portion, and it is easy to obtain high charge and discharge characteristics. However, sometimes a high withstand voltage cannot be ensured.

[0013] In the solid electrolyte layer formed by electrolytic polymerization, compared with the solid electrolyte layer formed using a liquid dispersion, the conjugated polymer and the dopant are highly dispersed, and high electronic conductivity is obtained. In addition, an increase in the resistance of the solid electrolyte layer due to the segregation of the polymer anions is suppressed. As a result, a low equivalent series resistance (ESR) and high cycle characteristics are obtained. However, it is known that the dielectric breakdown voltage is low.

[0014] In view of the above situation, (1) A solid electrolytic capacitor according to one aspect of the present disclosure includes at least one capacitor element. The capacitor element includes: an anode foil having a porous portion at least on the surface layer; a dielectric layer covering at least a part of the anode foil; and a solid electrolyte layer covering at least a part of the dielectric layer. The solid electrolyte layer includes a first polymer component containing a conjugated polymer and a second polymer component containing a polymer anion. In the Raman spectrum of the surface layer of the solid electrolyte layer, a peak peculiar to the first polymer component is observed. When the rated voltage of the solid electrolytic capacitor is set to Rv (unit: V), the average thickness T of the dielectric layer is 2.50×Rv (unit: nm) or more.

[0015] In the configuration of (1) above, by setting the average thickness T of the dielectric layer to 2.50 times or more of the rated voltage of the solid electrolytic capacitor, the dielectric breakdown voltage during the formation of the solid electrolyte layer by electrolytic polymerization can be improved, and high withstand voltage characteristics can be ensured. Generally, if the thickness of the dielectric layer increases, the capacitance of the solid electrolytic capacitor tends to decrease. However, in the solid electrolytic capacitor of the present disclosure, the solid electrolyte layer is formed by electrolytic polymerization, thereby compensating for the decrease in capacitance accompanying the increase in the thickness of the dielectric layer, obtaining a sufficiently high capacitance, and suppressing the decrease in capacitance even during repeated charge and discharge. Even for capacitors with a rated voltage of 12V or more, which is generally high voltage, dielectric breakdown during voltage application can be suppressed.

[0016] (2) In the configuration of (1) above, the solid electrolyte layer may contain sulfur (S) element, and the anode foil may contain aluminum (Al) element. The solid electrolyte layer has: a first part filled in the pores of the porous part of the anode foil having a dielectric layer and a second part disposed outside the anode foil on the side closer to the main surface of the anode foil having a dielectric layer. In the element mapping obtained by using an Electron Probe Micro Analyzer (EPMA) of the cross-section of the porous part, when the presence ratio of the Al element in the porous part is set to 100%, the presence ratio of the S element in the porous part may be 0.5% or more. In this case, the decrease in capacitance during repeated charge and discharge can be further suppressed.

[0017] The S element mainly originates from the conjugated polymer and dopant constituting the solid electrolyte. For example, the conjugated polymer of the polythiophene series contains the S element of the thiophene ring, and the dopant contains the S element derived from anionic groups such as sulfonic groups. On the other hand, the anode foil containing the Al element is mainly composed of aluminum or an aluminum alloy, and the dielectric layer is composed of aluminum oxide. Therefore, the relatively larger presence ratio of the S element compared to the presence ratio of the Al element in the porous part means that the ratio of the solid electrolyte contained in the porous part is relatively larger (in other words, the filling rate of the solid electrolyte in the pores of the porous part is higher). In the present disclosure, it is considered that by setting the presence ratio of the S element in the porous part within the above range, a relatively high filling rate of the solid electrolyte is obtained, the flow path of air becomes less, and the progress of deterioration of the solid electrolyte is hindered. In addition, it is considered that since the solid electrolyte is highly filled in the pores of the porous part, even if the solid electrolyte undergoes repeated volume changes due to repeated charge and discharge, a relatively large number of contacts are maintained between the first part and the second part or between the porous part and the second part. Therefore, it is considered that a relatively high capacitance can be maintained even during repeated charge and discharge.

[0018] The above-described higher S element content rate in the porous portion is obtained, for example, as follows: A dielectric layer is formed on the surface of an anode foil containing an Al element and having a porous portion at least on the surface layer. The obtained anode foil having a dielectric layer on the surface is immersed in a polymerization solution containing a precursor of a conjugated polymer and a polymeric anion containing an S element, and electrolytic polymerization is carried out in a three-electrode system at a relatively low polymerization potential, whereby the above-described higher S element content rate in the porous portion is obtained. It is considered that by carrying out electrolytic polymerization under such specific conditions, in the presence of a polymeric anion having relatively high stability as a dopant, the polymerization of the precursor of the conjugated polymer proceeds slowly, and a conductive polymer formed by the interaction between the conjugated polymer and the polymeric anion is generated to form a dense solid electrolyte. Since the precursor and the polymeric anion are in a state dissolved in the polymerization solution, they easily enter the deep part of the fine pores of the porous portion. Therefore, polymerization easily occurs not only near the opening of the pores but also in the deep part of the pores. Thus, it is considered that a high filling rate of the solid electrolyte in the pores is obtained. In the pores of the porous portion, the polymerization of the precursor of the conjugated polymer proceeds while interacting with the polymeric anion. Therefore, it is easy to obtain a high orientation of the formed conjugated polymer, and the polymeric anion is in a relatively uniformly dispersed state, and a relatively high doping rate is easily obtained. Therefore, high conductivity of the solid electrolyte in the first portion is obtained, and even when charge and discharge are repeated, de-doping or deterioration of the conjugated polymer is less likely to occur. In addition, since the filling rate of the solid electrolyte in the porous portion is high, even if the solid electrolyte undergoes repeated volume changes due to repeated charge and discharge, the contact between the first portion or the porous portion and the second portion is maintained. Thus, it is considered that the above-described excellent effects are obtained.

[0019] It should be noted that even when a liquid dispersion containing a conjugated polymer containing an S element such as poly(3,4-ethylenedioxythiophene) (PEDOT) and a polymeric anion containing an S element such as polystyrene sulfonic acid (PSS) is used to form the first portion, the presence ratio of the S element in the porous portion is low, for example, less than 0.5%. It is considered that this is because, as described above, even when a liquid dispersion is used, the filling rate of the solid electrolyte in the porous portion is low.

[0020] Three - electrode electrolytic polymerization is carried out using three electrodes: an anode foil on which a dielectric layer is formed on the surface, a counter electrode, and a reference electrode. In three - electrode electrolytic polymerization, by using the reference electrode, the potential of the anode can be precisely controlled without being affected by the change in the natural potential of the counter electrode. In the three - electrode case, the electrolytic polymerization reaction can be controlled more precisely compared to the two - electrode case using the anode foil and the counter electrode. In addition, it is considered that while interacting with polymer anions within a specified range of polymerization potential, the polymer chains grow slowly. As a result, it is considered that the orientation of the formed conjugated polymer is improved, and the dispersion of polymer anions is increased, and a more uniform and denser solid electrolyte is formed with a high filling rate within the pores of the porous part. In addition, it is considered that by highly dispersing polymer anions, a higher doping rate is easily obtained, and the conductivity of the solid electrolyte itself is easily increased.

[0021] (3) In the configuration of (1) or (2) above, the average thickness T of the dielectric layer can be 3.5×Rv (nm) or less. In this case, a higher capacitance is obtained.

[0022] (4) In the configuration of any one of (1) to (3) above, the rated voltage Rv of the solid electrolytic capacitor can be 12V or more. According to the present disclosure, a solid electrolytic capacitor capable of withstanding high - voltage applications with a high rated voltage can be obtained.

[0023] (5) In the configuration of any one of (1) to (4) above, the conjugated polymer can contain monomer units corresponding to thiophene compounds. In this case, by adjusting the conditions of electrolytic polymerization, electrolytic polymerization is easily carried out even in the presence of polymer anions containing S elements, which is more advantageous for increasing the charging rate of the conductive polymer in the pores of the porous part.

[0024] (6) In the configuration of (5) above, the peak peculiar to the first polymer component can include a first peak observed in the wavenumber range of 1200 cm -1 or more and 1600 cm -1 or less. The first peak is attributed to the C═C stretching vibration of the thiophene ring in the monomer unit corresponding to the thiophene compound. By clearly observing the first peak, it can be known that the segregation of polymer anions is suppressed. In the solid electrolyte layer, the conjugated polymer and polymer anions are highly dispersed, thereby obtaining higher charge - discharge characteristics.

[0025] (7) In the configuration of (5) or (6) above, the first polymer component can at least contain monomer units corresponding to 3,4 - ethylenedioxythiophene compounds as monomer units corresponding to thiophene compounds. In this case, higher conductivity of the solid electrolyte layer is easily obtained, and higher charge - discharge characteristics can be ensured.

[0026] (8) In the configuration of any one of the above (1) to (7), the weight average molecular weight Mw of the polymeric anion can be 100 or more and 500,000 or less. In this case, in the first part, it is easy to obtain a higher dispersibility and a relatively high doping rate of the polymeric anion, which is advantageous for ensuring a higher conductivity of the solid electrolyte layer. Also, it is easy to obtain high stability of the dopant and the solid electrolyte.

[0027] (9) The polymeric anion can contain monomer units corresponding to an organic sulfonic acid compound. Even when using such a polymeric anion, it is possible to highly fill the solid electrolyte in the porous portion, so it is easy to obtain a high conductivity of the solid electrolyte layer and it is easy to maintain a relatively high capacity even during repeated charge and discharge.

[0028] (10) In the configuration of any one of the above (1) to (9), the peak peculiar to the first polymer component can include a first peak observed in the wavenumber range of 1200 cm -1 or more and 1600 cm -1 or less. The polymeric anion can contain monomer units corresponding to an aromatic sulfonic acid compound. In the Raman spectrum of the surface layer of the solid electrolyte layer, a second peak peculiar to the second polymer component can be observed in the wavenumber range of 800 cm -1 or more and 1100 cm -1 or less. The ratio (= I p1 / I p2 ) of the intensity I p1 of the first peak to the intensity I p2 of the second peak can be 2 or more. When the ratio of I p1 / I p2 is in this range, the orientation and crystallinity of the conjugated polymer in the second part are relatively high. Therefore, it is easy to ensure a high conductivity of the solid electrolyte in the second part.

[0029] (11) Regarding any one of the configuration of the above (2) and the case of the configuration of the above (3) to (10) related to the above (2), in the Raman spectrum of the first part, the ratio (= I p1 / I p2 ) of the intensity I p1 of the first peak peculiar to the first polymer component to the intensity I p2 of the second peak peculiar to the second polymer component can be 2 or more. When the ratio of I p1 / I p2 is in this range, the orientation and crystallinity of the conjugated polymer in the first part are relatively high. Therefore, it is easy to ensure a high conductivity of the solid electrolyte in the first part.

[0030] (12) In the configuration of any one of the above (1) to (11), the solid electrolytic capacitor may include a plurality of stacked capacitor elements. In this case, a higher capacitance can be obtained, and the filling rate of the solid electrolyte into the pores of the porous portion is high. Thus, a high capacitance can be maintained even when repeatedly charged and discharged.

[0031] Hereinafter, including the configurations of the above (1) to (12), the solid electrolytic capacitor of the present disclosure will be described in more detail. As long as at least one selected from the constituent elements described below can be combined technically, it can be arbitrarily combined with at least one of the configurations of the above (1) to (12) of the solid electrolytic capacitor of the present disclosure.

[0032] [Solid electrolytic capacitor]

[0033] The solid electrolytic capacitor includes one or two or more capacitor elements.

[0034] [Capacitor element]

[0035] The capacitor element includes: an anode foil; a dielectric layer covering at least a part of the anode foil; and a cathode portion covering at least a part of the dielectric layer. The cathode portion includes a solid electrolyte layer covering at least a part of the dielectric layer.

[0036] (Anode foil)

[0037] The anode foil included in the capacitor element may include valve action metals, alloys containing valve action metals, and compounds containing valve action metals, etc. The anode foil may include one of these materials or a combination of two or more. As valve action metals, for example, aluminum (Al), tantalum, niobium, and titanium can be cited. The anode foil may include at least aluminum. The anode foil may include aluminum metal, may include aluminum alloy, or may include both.

[0038] The anode foil includes a porous portion at least on the surface layer. The porous portion includes many fine pores. Through the porous portion, the anode foil has a fine uneven shape at least on the surface, the surface area becomes larger, and a high capacitance is obtained. The porous portion can be formed, for example, by roughening the surface of the metal foil. For example, the anode foil may have a core portion and porous portions formed on two surfaces of the core portion and continuous with the core portion. The porous portion is the outer portion of the roughened metal foil, and the remaining portion as the inner portion of the metal foil is the core portion. The porous portion may be formed on a part of the surface layer of the anode foil or on the entire surface layer.

[0039] The roughening can be performed by an etching process or the like. The etching process can be performed by electrolytic etching or chemical etching. For example, in the case of electrolytic etching, the thickness of the porous portion, the shape and size of the pores, etc. can be adjusted by etching conditions (the number of steps and time of the etching process, current density, composition and temperature of the etching solution, etc.).

[0040] The anode foil has a first end portion and a second end portion on the side opposite to the first end portion. The solid electrolyte layer is formed on a portion of the second end portion side of the anode foil with a dielectric layer interposed therebetween. The portion of the second end portion side of the anode foil on which the cathode portion including the solid electrolyte layer is formed is sometimes referred to as the cathode formation portion. The anode foil has a porous portion at least on the surface layer of the cathode formation portion, for example. The portion of the first end portion side of the anode foil on which the cathode portion is not formed is sometimes referred to as the anode lead-out portion. The anode lead-out portion is used to electrically connect to an external electrode on the anode side, for example. An anode lead terminal may be connected to the anode lead-out portion.

[0041] In this specification, the direction from the first end portion toward the second end portion in a state where the anode foil is flat is sometimes referred to as the longitudinal direction of the anode foil. The direction from the first end portion side toward the second end portion side is a direction parallel to the straight line direction connecting the center of the end face of the first end portion and the center of the end face of the second end portion. This direction is sometimes referred to as the longitudinal direction of the anode foil or the capacitor element.

[0042] (Dielectric layer)

[0043] The dielectric layer is formed so as to cover at least a part of the surface of the anode foil. The dielectric layer is an insulating layer that functions as a dielectric. The dielectric layer is formed by anodizing the valve action metal on the surface of the anode foil by using chemical conversion treatment or the like. In the dielectric layer formed on the surface of the anode foil having a porous portion, the surface of the dielectric layer has a fine uneven shape according to the shape of the surface of the porous portion.

[0044] In the present disclosure, when the rated voltage of the solid electrolytic capacitor is Rv (V), the average thickness T of the dielectric layer is 2.50×Rv (nm) or more. By the dielectric layer having such an average thickness, excellent withstand voltage of the solid electrolytic capacitor is obtained, and dielectric breakdown when a high voltage is applied can be suppressed. In addition, in the present disclosure, the high conductivity of the solid electrolyte layer is ensured, and oxidative deterioration is suppressed. Therefore, even if the average thickness T of the dielectric layer is in the above range, a relatively high initial capacitance can be ensured, and a high capacitance can be maintained even when charging and discharging are repeated. From the viewpoint of ensuring a higher capacitance, the average thickness T may be 3.50×Rv or less, may be 3.00×Rv or less, and may also be 2.75×Rv or less.

[0045] The thickness of the dielectric layer is determined through the following steps. For the measurement sample, using an electron microscope (FE-SEM, Hitachi Regulus8230), secondary electron images are taken of 3 fields of view under the conditions of an acceleration voltage of 2.0 kV and a magnification of 100k times. The dielectric thickness at 10 locations in each field of view is measured and averaged, thereby determining the thickness of the dielectric layer. In the cross-section of the measurement sample, images are taken of 3 fields of view: (i) the boundary between the second part and the porous part and its vicinity, (ii) the vicinity of the center of the thickness of the porous part, and (iii) the part on the core side of the anode foil of the porous part.

[0046] The measurement sample is fabricated through the following steps. At the midpoint in the length direction of the capacitor element, the capacitor element or solid electrolytic capacitor is cut using a wire saw to expose the cross-section. Using a cross-section polisher (CP, Cross section Polisher, JEOL model SM-09010), the exposed cross-section is processed under the conditions of an output power of 6.0 kV and a processing time of 10 h. Thus, the above-mentioned measurement sample is obtained.

[0047] The dielectric layer can also be formed from a material that functions as a dielectric layer. For example, the dielectric layer contains an oxide of a valve metal as such a material. For example, when tantalum is used as the valve metal, the dielectric layer contains Ta2O5, and when aluminum is used as the valve metal, the dielectric layer contains Al2O3. However, the dielectric layer is not limited to these specific examples.

[0048] In the case where the dielectric layer is formed through chemical conversion treatment, the chemical conversion treatment is carried out, for example, by immersing the anode foil in a chemical conversion solution and applying a voltage. The average thickness T of the dielectric layer can be adjusted by regulating the concentration of the chemical conversion solution, the composition of the chemical conversion solution, the voltage applied during chemical conversion, the chemical conversion temperature, and the chemical conversion time, etc.

[0049] Examples of the chemical conversion solution include, for example, an aqueous solution containing a salt. Examples of the salt include phosphates, adipates, and borates. Examples of the cations constituting the salt include ammonium cations, alkali metal cations, etc. Examples of phosphates include ammonium phosphate salts, potassium phosphate salts, sodium phosphate salts, etc. Examples of ammonium phosphate salts include diammonium hydrogen phosphate, ammonium dihydrogen phosphate, etc. The chemical conversion solution can contain one kind of salt or can contain two or more kinds of salts in combination. From the viewpoints of workability, etc., ammonium dihydrogen phosphate aqueous solution and other ammonium phosphate aqueous solutions, ammonium adipate aqueous solution, etc. are preferred.

[0050] The salt concentration in the chemical conversion solution may be 0.2 mass % to 0.4 mass % or 0.25 mass % to 0.35 mass %. When the salt concentration is within such a range, a relatively large average thickness T is easily obtained, and the precipitation of excessive salt is suppressed, which can reduce product defects.

[0051] The voltage applied to the anode foil during chemical conversion can be greater than 2.00 times and less than 2.40 times the rated voltage Rv, or more than 2.05 times and less than 2.40 times, or more than 2.05 times and less than 2.30 times. When the voltage is in such a range, it is easy to obtain a relatively large average thickness T, and it is easy to obtain a good balance between high capacity and high voltage resistance.

[0052] The temperature of the chemical conversion solution during chemical conversion may be 60° C. to 80° C., or 65° C. to 75° C. When the temperature is within this range, a relatively large average thickness T is easily obtained, and excessive salt precipitation is suppressed, thereby reducing product defects.

[0053] The chemical conversion time may be 15 minutes to 90 minutes, 25 minutes to 60 minutes, or 30 minutes to 60 minutes. When the chemical conversion time is within such a range, high productivity is ensured and a relatively large average thickness T is easily obtained.

[0054] (Cathode)

[0055] The cathode portion at least includes a solid electrolyte layer covering at least a portion of the dielectric layer. The solid electrolyte layer is formed on the second end side of the anode foil through the dielectric layer. The cathode portion usually includes a solid electrolyte layer covering at least a portion of the dielectric layer and a cathode lead layer covering at least a portion of the solid electrolyte layer. The solid electrolyte layer and the cathode lead layer are described below.

[0056] (Solid electrolyte layer)

[0057] The solid electrolyte layer includes a first polymer component containing a conjugated polymer and a second polymer component containing a polymer anion. The solid electrolyte layer is divided into a first portion filled in the pores of the porous portion of the anode foil having the dielectric layer and a second portion arranged on the outside of the anode foil than the main surface of the anode foil having the dielectric layer.

[0058] The solid electrolyte layer is composed of a solid electrolyte (in other words, a conductive polymer). The conductive polymer includes a conjugated polymer and a dopant. The solid electrolyte may further contain an additive as required.

[0059] The solid electrolyte layer may contain sulfur (S) element. The S element contained in the solid electrolyte mainly comes from conductive polymers. More specifically, the S element is contained at least in the dopant, and may also be contained in both the dopant and the conjugated polymer. In addition, the S element is contained at least in the first part, and usually contained in both the first part and the second part.

[0060] When the anode foil contains aluminum (Al) element, in the porous part, when the presence ratio of the Al element is set to 100%, the presence ratio of the S element can be 0.5% or more, can also be 0.65% or more, and can further be 0.7% or more. By the presence ratio of the S element being in such a range, the highly conductive solid electrolyte is highly filled in the porous part. Therefore, the deterioration of the solid electrolyte during repeated charge and discharge is suppressed, the contact between the first part or the porous part and the second part can be maintained, and the reduction of the capacity can be suppressed. In addition, the resistance of the first part can be suppressed to be low from the initial stage, the initial equivalent series resistance (ESR) can be suppressed to be low, and a relatively high initial capacity can be ensured. Considering the volume of the pores in the porous part, the presence ratio of the S element is, for example, 5% or less. The presence ratio of each element is obtained by elemental mapping using electron probe microanalysis (EPMA) of the cross-section of the porous part.

[0061] The analysis using EPMA is performed using a sample in which the cross-section of the porous part of the part where the cathode part containing the solid electrolyte is formed in the capacitor element is exposed and a platinum film is formed. In the cross-sectional image of the porous part where the solid electrolyte is formed, for a region with a width of 5 μm including the bottom of the porous part starting from the main surface of the anode foil (in other words, the entire thickness of the porous part on one side of the anode foil × the width of 5 μm region), elemental mapping is performed based on the difference in the wavelength of the characteristic X-rays of EPMA, and the net intensity of the contained elements is measured. The net intensity is a value obtained by removing the background (noise) from the measured value of each element. The ratio (%) of the net intensity of the S element to the net intensity of the Al element when the net intensity of the Al element is set to 100% is obtained. For multiple regions (for example, 5 regions), the ratio (%) of the net intensity of the S element is obtained, and the average value is calculated as the presence ratio (%) of the S element when the presence ratio of the Al element in the porous part is set to 100%.

[0062] The conditions for EPMA analysis are as follows.

[0063] Environment during measurement: 25 °C, atmospheric pressure

[0064] Accelerating voltage: 15.0 kV

[0065] Beam current: 20.1 nA

[0066] Integration time: 180.0 ms / point (12-minute mode)

[0067] Spectroscopic crystal: AP / CH1, PbST / CH2, PET / CH3, LiF / CH4, LSA80 / CH5

[0068] A sample for analysis can be prepared, for example, through the following steps. First, a solid electrolytic capacitor is embedded in a curable resin and the curable resin is cured. At a specified position in the length direction of the capacitor element, wet grinding or dry grinding is performed on the obtained cured product in such a manner that a cross-section perpendicular to the length direction of the capacitor element and parallel to the thickness direction is exposed. Ion milling is used to smooth the exposed cross-section. On the smoothed cross-section, platinum (Pt) is sputtered using a sputtering device to form a platinum film with a thickness of 1 nm to 2 nm. Thus, a sample for analysis is obtained. It should be noted that when the length of the region where the solid electrolyte is formed in the direction parallel to the length direction of the capacitor element is set to 1, the cross-section is set to the cross-section at a position of 0 to 0.05 from the end on the second end side of the region where the solid electrolyte is formed.

[0069] (The first part)

[0070] The solid electrolyte of the first part is formed by electrolytic polymerization (especially three-electrode electrolytic polymerization). The first part may contain a first polymer component equivalent to a conjugated polymer and a second polymer component equivalent to a polymer anion containing an S element.

[0071] Examples of the conjugated polymer equivalent to the first polymer component include well-known conjugated polymers used in solid electrolytic capacitors, such as π-conjugated polymers. Examples of the conjugated polymer include polymers having a basic skeleton of polypyrrole, polythiophene, polyaniline, polyfuran, polyacetylene, polyphenylene, polyphenylene vinylene, polyacene, and polythiophene vinylene. The above polymers only need to contain at least one monomer unit constituting the basic skeleton. The monomer units also include monomer units having substituents. The above polymers also include homopolymers and copolymers of two or more monomers. For example, polythiophene includes PEDOT, etc.

[0072] From the viewpoint that electrolytic polymerization in the presence of a polymeric anion is easy to carry out, the conjugated polymer can include monomer units corresponding to thiophene compounds, monomer units corresponding to pyrrole compounds, or monomer units corresponding to aniline compounds. The conjugated polymer can include monomer units corresponding to thiophene compounds. Thiophene compounds generally have a higher polymerization potential than pyrrole compounds and are difficult to polymerize. In the present disclosure, a solid electrolyte layer is formed by three-electrode electrolytic polymerization. Therefore, even when a thiophene compound is used as a precursor, the polymerization reaction can proceed rapidly. Thus, even though a polymeric anion is used, the solid electrolyte containing the first polymer component and the second polymer component containing the polymeric anion can be highly filled in the fine recesses on the surface of the dielectric layer in a state where the respective polymer components are more uniformly dispersed.

[0073] The first polymer component can contain an S element. The conjugated polymer constituting such a first polymer component, for example, includes monomer units corresponding to thiophene compounds. When a thiophene compound is used as a precursor, by adjusting the conditions of electrolytic polymerization, electrolytic polymerization is easy to carry out even in the presence of a polymeric anion containing an S element, which is more advantageous in increasing the presence ratio of the S element in the first part. As the thiophene compound, a compound having a thiophene ring and capable of forming a repeating structure of the corresponding monomer unit can be cited. The thiophene compound can be linked at the 2-position and 5-position of the thiophene ring to form a repeating structure of monomer units.

[0074] The thiophene compound can, for example, have a substituent at at least one of the 3-position and 4-position of the thiophene ring. The substituent at the 3-position and the substituent at the 4-position can be linked to form a ring fused to the thiophene ring. As the thiophene compound, for example, thiophene having a substituent at at least one of the 3-position and 4-position, an alkylenedioxythiophene compound (such as an ethylenedioxythiophene compound, etc., C 2-4 alkylenedioxythiophene compounds, etc.) can be cited. The alkylenedioxythiophene compound also includes an alkylenedioxythiophene compound having a substituent in the alkyl part.

[0075] As the substituent, an alkyl group (such as a methyl group, an ethyl group, etc., C 1-4 alkyl groups, etc.), an alkoxy group (such as a methoxy group, an ethoxy group, etc., C 1-4 alkoxy groups, etc.), a hydroxyl group, a hydroxyalkyl group (such as a hydroxymethyl group, etc., hydroxy C 1-4 alkyl groups, etc.) are preferred, but are not limited to these. When the thiophene compound has two or more substituents, the respective substituents can be the same or different.

[0076] A conjugated polymer (such as PEDOT) containing at least monomer units corresponding to 3,4-ethylenedioxythiophene compounds (such as 3,4-ethylenedioxythiophene (EDOT)) can also be used. The conjugated polymer containing at least monomer units corresponding to EDOT can contain only monomer units corresponding to EDOT, or in addition to these monomer units, can also contain monomer units corresponding to thiophene compounds other than EDOT.

[0077] The weight-average molecular weight (Mw) of the conjugated polymer is not particularly limited, and is, for example, 1000 or more and 1000000 or less.

[0078] It should be noted that in this specification, the weight-average molecular weight (Mw) is a value in terms of polystyrene measured by gel permeation chromatography (GPC). It should be noted that GPC is usually measured using a polystyrene gel column and water / methanol (volume ratio 8 / 2) as the mobile phase.

[0079] The first part can contain a second polymer component equivalent to a polymer anion containing an S element as a dopant. Examples of the polymer anion constituting the second polymer component include polymers having a plurality of sulfo groups. By using the second polymer component, it is easy to increase the presence ratio of the S element in the first part. In addition, higher conductivity of the solid electrolyte layer can be ensured, and dedoping from the solid electrolyte layer can be easily suppressed. The polymer anion can have other anionic groups (such as carboxyl groups) in addition to the sulfo groups.

[0080] In the solid electrolyte, the anionic groups (such as sulfo groups and carboxyl groups) of the dopant can be included in a free form, anionic form, or salt form, or can be included in a form bonded or interacting with the conjugated polymer. In this specification, including all these forms, they are sometimes simply referred to as "anionic groups", "sulfo groups", or "carboxyl groups", etc.

[0081] The polymer anion can contain monomer units M1 corresponding to an organic sulfonic acid compound. The organic sulfonic acid compound can be any of aliphatic, alicyclic, aromatic, and heterocyclic types. The polymer anion can be a homopolymer containing only monomer units M1, or a copolymer containing monomer units M1 and other monomer units other than these.

[0082] As the polymer anion having a sulfo group, for example, polymeric poly-sulfonic acid can be mentioned. Specific examples of the polymer anion include polyvinylsulfonic acid, polystyrenesulfonic acid (including copolymers and substituted products having substituents, etc.), polyallylsulfonic acid, polyacrylic acid sulfonic acid, polymethacrylic acid sulfonic acid, poly(2-acrylamide-2-methylpropane sulfonic acid), polyisoprene sulfonic acid, polyester sulfonic acid (such as aromatic polyester sulfonic acid), and phenolsulfonic acid novolak resin. Among them, the polymer anion is not limited to these specific examples. The solid electrolyte may contain one kind of polymer anion, or may contain two or more kinds of polymer anions in combination.

[0083] Particularly when the polymer anion has an aromatic ring, high heat resistance is obtained. Therefore, even when the solid electrolytic capacitor is exposed to high temperature, dedoping is suppressed, and high conductivity of the solid electrolyte layer can be maintained. In the capacitor element of the present disclosure, even when a polymer anion having an aromatic ring is used, segregation of the polymer anion in the surface layer and the first part of the solid electrolyte layer is suppressed, and a more uniform dispersion state of the first polymer component and the second polymer component in the solid electrolyte layer can be ensured. Moreover, such an excellent dispersion state can be confirmed by Raman spectroscopy.

[0084] As the polymer anion having an aromatic ring, for example, the polymer anion having an aromatic ring in the polymer anion containing a monomer unit M1 corresponding to an organic sulfonic acid compound can be mentioned. As such a polymer anion, preferably, at least a monomer unit corresponding to an aromatic sulfonic acid compound (sometimes referred to as monomer unit M2) is included as monomer unit M1, etc. As such a polymer anion, for example, polystyrenesulfonic acid (including copolymers and substituted products having substituents, etc.), aromatic polyester sulfonic acid, and phenolsulfonic acid novolak resin among the above polymer anions can be mentioned, but are not limited thereto.

[0085] The Mw of the polymer anion is, for example, 100 or more and 500,000 or less. From the viewpoint of easily highly filling the pores of the porous part with the conductive polymer, the Mw of the polymer anion constituting the first part is preferably 100,000 or less, more preferably 1,000 or more and 100,000 or less or 10,000 or more and 100,000 or less. In addition, when the Mw of the polymer anion is in such a range, in the first part, higher dispersibility and higher doping rate of the polymer anion are easily obtained, which is advantageous for ensuring higher conductivity. And high stability of the dopant and the conductive polymer is easily obtained.

[0086] In the first part, the amount of the dopant contained in the solid electrolyte is, for example, 10 parts by mass or more and 1000 parts by mass or less, and may be 20 parts by mass or more and 500 parts by mass or less, relative to 100 parts by mass of the conjugated polymer. From the viewpoint of easily obtaining higher dispersibility of the polymer anion and a relatively high doping rate, it may be 50 parts by mass or more and 200 parts by mass or less.

[0087] (Method for forming a solid electrolyte layer)

[0088] The first part can be formed by electrolytic polymerization of a precursor of a conjugated polymer in the presence of a dopant in a three-electrode system on the surface of the dielectric layer. For example, electrolytic polymerization is carried out in a state where the cathode forming portion of an anode foil having a dielectric layer formed on its surface is immersed in a liquid composition (polymerization solution) containing a precursor of a conjugated polymer and a dopant. By adjusting the conditions of electrolytic polymerization, the fine pores of the porous portion can be highly filled with the solid electrolyte, and the presence ratio of S element can be increased. In addition, the dopant can be doped at a relatively high doping rate, high conductivity of the first part can be ensured, and the conjugated polymer can be stabilized in terms of energy. Thereby, deterioration of the solid electrolyte in the first part can be suppressed, and peeling from the second part is also suppressed even during repeated charge and discharge, so that high conductivity of the entire solid electrolyte layer can be obtained and high capacity can be ensured.

[0089] Examples of the precursor of the conjugated polymer include raw material monomers of the conjugated polymer, oligomers formed by linking multiple molecular chains of the raw material monomers, and prepolymers. One type of precursor can be used, or two or more types can be used in combination. From the viewpoint of easily obtaining higher orientation of the conjugated polymer, as the precursor, it is preferably at least one selected from the group consisting of monomers and oligomers (especially monomers).

[0090] The liquid composition usually contains a solvent. Examples of the solvent include water, organic solvents, and mixed solvents of water and organic solvents (water-soluble organic solvents, etc.).

[0091] When using other conductive materials, additives, etc., they can also be added to the liquid composition.

[0092] The liquid composition may contain an oxidizing agent as needed. In addition, the oxidizing agent can be coated on the anode foil before or after bringing the liquid composition into contact with the anode foil having a dielectric layer formed thereon. Examples of such an oxidizing agent include compounds capable of generating Fe 3+ (iron sulfate, etc.), persulfates (sodium persulfate, ammonium persulfate, etc.), and hydrogen peroxide. The oxidizing agent can be used alone or in combination of two or more.

[0093] The three-pole electrolytic polymerization is carried out by immersing the anode foil, the counter electrode and the reference electrode in the liquid composition. As the counter electrode, for example, a Ti electrode is used, but it is not limited to this. As the reference electrode, a silver / silver chloride electrode (Ag / Ag + ).

[0094] In electrolytic polymerization, the voltage applied to the anode foil (polymerization voltage) is, for example, greater than 0.6V and less than 1.5V. From the viewpoint of being easy to highly fill the pores of the porous portion and to ensure relatively high crystallinity of the solid electrolyte, the polymerization voltage is preferably greater than 0.9V and less than 1.2V (or less than 1.1V), and may also be greater than 1V and less than 1.2V (or less than 1.1V). By performing electrolytic polymerization in a three-pole manner at such a polymerization voltage, the polymerization reaction in the pores can be precisely controlled. Thus, in the pores, the polymer chains of the conjugated polymer can be grown in a state where the dopant is highly dispersed, and the solid electrolyte can be highly filled in the pores. In addition, since the polymerization can be carried out slowly, the orientation and crystallinity of the conjugated polymer can be further improved, and a relatively high doping rate can be obtained, making it easy to ensure relatively high conductivity. It should be noted that the polymerization voltage is relative to the reference electrode (silver / silver chloride electrode (Ag / Ag + )) The potential of the anode foil. In electrolytic polymerization, a power supply (power supply belt, etc.) is electrically connected to the anode lead-out portion, and a voltage is applied to the anode foil via the power supply. The potential of the anode foil refers to the potential of the power supply electrically connected to the anode foil.

[0095] The temperature for performing the electrolytic polymerization is, for example, 5° C. to 60° C., or 15° C. to 35° C.

[0096] Before electrolytic polymerization, a pre - coating can be formed on the surface of the dielectric layer. The pre - coating contains, for example, a conductive material. The pre - coating can be formed using a liquid dispersion containing a conductive polymer (such as a conjugated polymer and a dopant, etc.). Among them, compared with the liquid dispersion used to form the solid electrolyte constituting the cathode portion, the particle size of the conductive polymer in the liquid dispersion used for forming the pre - coating is small and the concentration is low. For example, the average primary particle size of the particles of the conductive polymer contained in the liquid dispersion for the pre - coating is, for example, 100 nm or less, and can also be 60 nm or less. In addition, the dry solid content concentration of the liquid dispersion is, for example, 1.2 mass% or less. It should be noted that in the liquid dispersion used to form the solid electrolyte constituting the cathode portion, the average primary particle size of the particles of the conductive polymer is usually 200 nm or more, and the dry solid content concentration is 2 mass% or more. The conjugated polymer of the pre - coating and the conjugated polymer formed by electrolytic polymerization can be of the same type or different types. The dopant of the pre - coating and the dopant used in electrolytic polymerization can be the same or different. In the present disclosure, since the first part is formed by electrolytic polymerization, even if a liquid dispersion is used to form the pre - coating, the polymerization liquid can fully penetrate into the fine pores, and the first part can be formed with a high filling rate.

[0097] (Second part)

[0098] The second part can be different from at least one of the composition and the film quality of the solid electrolyte of the first part, or can be the same in both composition and film quality. In the case where the solid electrolyte as a whole is composed of multiple layers, the first part can be the first layer and the second part can be the second layer. In this case, at least one of the composition and the film quality of the first layer and the second layer can be different, or can be the same in both composition and film quality. In addition, the second part can also be composed of multiple layers. At least two layers in the multiple layers can be different from at least one of the composition and the film quality, or can be the same in both.

[0099] The solid electrolyte of the second part is formed by electrolytic polymerization (especially three - electrode electrolytic polymerization) according to the situation of the first part. Thus, in the Raman spectrum of the surface layer of the solid electrolyte layer, a peak unique to the first polymer component is observed, and high crystallinity and high orientation of the conjugated polymer are obtained. In the whole solid electrolyte of the second part, the dopant is highly dispersed, it is easy to ensure high conductivity, and it is easy to suppress the deterioration of the solid electrolyte.

[0100] As the conjugated polymer contained in the second part, it can be selected from the conjugated polymers described for the first part, for example. The Mw of the conjugated polymer can be selected from the range described for the first part. As the dopant, at least one selected from the group consisting of the polymer anions and anions described for the first part can be used. Examples of the anion include, but are not particularly limited to, sulfate ion, nitrate ion, phosphate ion, borate ion, organic sulfonate ion, carboxylate ion, etc. Examples of the dopant that generates sulfonate ion include p-toluenesulfonic acid and naphthalenesulfonic acid. From the viewpoint of easily obtaining higher stability, a polymer anion is preferably used.

[0101] The Mw of the polymer anion can be selected from the range described for the first part.

[0102] The Mw of the polymer anion can be determined for a sample collected from a capacitor element or a solid electrolytic capacitor. More specifically, the GPC measurement can be performed using a sample collected through the following steps. First, the cured product obtained through the same steps as those for the measurement sample in the Raman spectroscopy measurement described later is subjected to grinding treatment or cross-section polishing to expose the solid electrolyte layer. The solid electrolyte is scraped from the solid electrolyte layer, and the polymer anion is extracted with hot water at 80°C or higher and 100°C or lower. The sample for measurement is obtained by concentrating the extract.

[0103] The amount of the dopant contained in the solid electrolyte is, for example, 10 parts by mass or more and 1000 parts by mass or less, 20 parts by mass or more and 500 parts by mass or less, or 50 parts by mass or more and 200 parts by mass or less with respect to 100 parts by mass of the conjugated polymer.

[0104] The polymerization voltage for electrolytic polymerization when forming the second part can be within the range described for the first part, can be 0.6 V or higher and 1.5 V or lower, or can also be 0.7 V or higher and 1.2 V or lower.

[0105] (Raman spectroscopy)

[0106] In the solid electrolytic capacitor of the present disclosure, in the Raman spectrum of the surface layer of the solid electrolyte layer, a first peak characteristic of a first polymer component (conjugated polymer) is observed. The main component of the solid electrolyte layer is a conjugated polymer. In the Raman spectrum of the surface layer of the solid electrolyte layer, the peak (first peak) attributed to the C═C stretching vibration of the conjugated polymer has the highest height and is characteristic. In the surface layer, the solid electrolyte exhibits high crystallinity due to the high orientation of the conjugated polymer. In addition, in the surface layer, the conjugated polymer is in an energetically stabilized state. Therefore, the surface layer exhibits a characteristic Raman spectrum in which the above-mentioned first peak is observed. In addition, in the Raman spectrum of the surface layer of the solid electrolyte layer, a second peak characteristic of a second polymer component is also observed.

[0107] For example, when the conjugated polymer contains a monomer unit corresponding to a thiophene compound, in the Raman spectrum of the surface layer of the solid electrolyte layer, the first peak is observed in the wavenumber range of 1200 cm -1 or higher and 1600 cm -1 or lower. The first peak is attributed to the C═C stretching vibration of the thiophene ring in the monomer unit corresponding to the thiophene compound. In addition, when the polymer anion contains a monomer unit corresponding to an aromatic sulfonic acid compound, in the Raman spectrum of the surface layer, the second peak is observed in the wavenumber range of 800 cm -1 or higher and 1100 cm -1 or lower. The second peak is attributed to the C-S stretching vibration between the aromatic ring and the S element of the sulfonyl group in the monomer unit corresponding to the aromatic sulfonic acid compound. For example, when the conjugated polymer contains at least a monomer unit corresponding to EDOT, the wavenumber of the position of the first peak is, for example, 1400 cm -1 or higher and 1450 cm -1 or lower, and can be 1410 cm -1 or higher and 1435 cm -1 or lower. When the polymer anion contains at least polystyrene sulfonic acid, the wavenumber of the position of the second peak is, for example, 900 cm -1 or higher and 1050 cm -1 or lower, and can be 950 cm -1 or higher and 1050 cm -1 .

[0108] On the other hand, in the Raman spectrum of the surface layer of the solid electrolyte layer formed using the liquid dispersion, the characteristic peak as described above is not observed. It is considered that this is because the fluorescence emission hinders the observation of the Raman scattered light. In the preparation of the liquid dispersion, polymerization is carried out in the liquid phase. Therefore, it is considered that in the obtained particles of the conductive polymer, polymer anions with a higher molecular weight are more likely to segregate on the surface compared to the precursor of the conjugated polymer. When using the liquid dispersion, the particles of the conductive polymer with polymer anions segregated on the surface are applied to the surface of the anode foil that also includes the porous portion. Therefore, it is considered that in the Raman spectrum of the surface layer of the solid electrolyte layer, due to the fluorescence emission caused by the segregated polymer anions, the characteristic peak as described above is not observed.

[0109] In the capacitor element of the present disclosure, in the Raman spectrum of the surface layer of the solid electrolyte layer, the intensity I of the first peak characteristic of the first polymer component (conjugated polymer) p1 relative to the intensity I of the second peak characteristic of the second polymer component (polymer anion) p2 ratio: I p1 / I p2 can be 2 or more, or can be 3 or more or 4 or more. When the I p1 / I p2 ratio is in this range, the orientation and crystallinity of the conjugated polymer in the surface layer of the solid electrolyte layer are relatively high. In this case, it can be said that the orientation and crystallinity of the conjugated polymer in the second part are also relatively high. Therefore, it is easy to ensure the high conductivity of the solid electrolyte in the second part. From the viewpoint of easily ensuring higher crystallinity and conductivity in the second part, the I p1 / I p2 ratio can be 5 or more or 5.5 or more. The I p1 / I p2 ratio is, for example, 10 or less. From the viewpoint of easily ensuring higher conductivity by obtaining a relatively high doping rate, the I p1 / I p2 ratio is preferably 7 or less. The I p1 / I p2 ratio is, for example, 2 or more and 10 or less (or 7 or less), or can be 4 or more and 10 or less (or 7 or less). In these numerical ranges, the lower limit value can also be replaced with the above value. It should be noted that the intensity of each peak corresponds to the peak height obtained by subtracting the background height from the height of each peak.

[0110] In the present disclosure, even the solid electrolyte formed in the pores of the porous portion obtains the orientation and crystallinity of the conjugated polymer and can ensure high conductivity. Therefore, in the first part, a Raman spectrum similar to that of the surface layer of the solid electrolyte layer is also observed. In the Raman spectrum of the first part, the intensity I of the first peakp1 Ratio of the intensity I relative to the second peak p2 : I p1 / I p2 can be selected from the above range of I p1 / I p2 in the Raman spectrum of the surface layer.

[0111] It should be noted that in the Raman spectrum of the surface layer of the solid electrolyte layer, sometimes a peak (sometimes referred to as the third peak) characteristic of the first polymer component is also observed in the wavenumber range of 2750 cm -1 or higher and 3000 cm -1 or lower. Compared with the first peak, the height of the third peak is small, but it is not hindered by the fluorescence emission of the segregated polymer anions, so it can be clearly observed. The wavenumber range where the third peak is observed can be 2800 cm -1 or higher and 3000 cm -1 or lower, or 2800 cm -1 or higher and 2900 cm -1 or lower. For example, when using PEDOT as the first polymer component, the third peak is observed in the wavenumber range of 2800 cm -1 or higher and 2900 cm -1 or lower.

[0112] In this specification, the Raman spectra of the surface layer and the first part of the solid electrolyte layer are measured for the solid electrolyte of the cross-section at a specified position in the solid electrolytic capacitor or the capacitor element under the following conditions. In this specification, the surface layer of the solid electrolyte layer refers to the part from the surface of the solid electrolyte layer to a depth of 100 nm. The Raman spectrum of the first part is measured for the solid electrolyte present in the pores of the porous part.

[0113] Raman spectrometer: RamanFORCE PAV of NanoPhoton Co., Ltd.

[0114] Diffraction grating: 600 gr / cm

[0115] Measured wavenumber range: 0 cm -1 or higher and 2500 cm -1 or lower

[0116] Temperature: 25 °C

[0117] The irradiation laser wavelength, laser output density, and exposure time are determined according to the type of conjugated polymer. For example, when the conjugated polymer is PEDOT, the irradiation laser wavelength is 784.73 nm, the laser output density is 870 W / cm 2 , and the exposure time is 60 seconds.

[0118] In the measurement of Raman spectra, a sample collected through the following steps can be used. First, a solid electrolytic capacitor is buried in a curable resin and the curable resin is cured. By grinding the cured product or performing cross-section polishing, a cross-section perpendicular to the length direction and parallel to the thickness direction of the capacitor element is exposed. When the length of the region where the solid electrolyte is formed in the direction parallel to the length direction of the capacitor element is set to 1, the cross-section is set to the cross-section at a position of 0 to 0.05 starting from the end on the side opposite to the anode lead-out portion (the end on the second end side) of the region where the solid electrolyte is formed. In this way, a sample for measurement is obtained. In the exposed cross-section of the sample, the Raman spectrum is measured for a 8 μm × 8 μm region of the solid electrolyte (the first part) formed in the pits on the surface of the porous part. The intensities of the first peak and the second peak are obtained by averaging the measured values at 12 positions of the 8 μm × 8 μm region of the first part formed in the pits of the porous part.

[0119] (Other)

[0120] The first part and the second part can each further contain, if necessary, at least one selected from the group consisting of known additives and known conductive materials other than conductive polymers. As the conductive material, for example, at least one selected from the group consisting of conductive inorganic materials such as manganese dioxide and TCNQ complex salts can be cited.

[0121] As the additive, known additives added to the solid electrolyte (such as coupling agents, silane compounds), known conductive materials other than conductive polymers, and water-soluble polymers can be cited. The first part and the second part can each contain one of these additives, or can contain two or more of these additives in combination. In the case where each part is composed of multiple layers, the additives contained in each layer can be the same or different.

[0122] The first part and the second part can each be a single layer or can be composed of multiple layers. In the case where each part is composed of multiple layers, the types, compositions, contents, etc. of the conductive polymers, additives, etc. contained in each layer can be the same or different. A layer for improving adhesion can be interposed between the dielectric layer and the solid electrolyte.

[0123] (Cathode lead-out layer)

[0124] The cathode lead-out layer only needs to have at least the first layer that contacts the solid electrolyte layer and covers at least a part of the solid electrolyte layer, and can also have the first layer and the second layer that covers at least a part of the first layer.

[0125] As the first layer, for example, a layer containing conductive particles, a metal foil, etc. can be cited. As the conductive particles, for example, at least one selected from conductive carbon and metal powder can be cited. For example, the cathode lead-out layer can be constituted by a layer containing conductive carbon (carbon layer) as the first layer and a layer containing metal powder or a metal foil as the second layer. In the case of using a metal foil as the first layer, the cathode lead-out layer can also be constituted by the metal foil.

[0126] As the conductive carbon, for example, graphite (artificial graphite, natural graphite, etc.) can be cited.

[0127] The layer containing metal powder as the second layer can be formed, for example, by laminating a composition containing metal powder on the surface of the first layer. As such a second layer, for example, a metal particle-containing layer formed using a paste containing metal powder and a resin binder can be cited. As the resin binder, a thermoplastic resin can also be used, but a thermosetting resin such as an imide-based resin or an epoxy resin is preferably used. From the viewpoint of easily obtaining high conductivity of the second layer, silver-containing particles can be used as the metal powder. As the silver-containing particles, silver particles and silver alloy particles, etc. can be cited. The second layer can contain one kind of silver-containing particle, or can contain two or more kinds in combination. The silver particles can contain a small amount of impurities.

[0128] In the case of using a metal foil as the first layer, the type of metal is not particularly limited. The metal foil preferably uses a valve-acting metal (aluminum, tantalum, niobium, etc.) or an alloy containing a valve-acting metal. If necessary, the surface of the metal foil can be roughened. A chemical conversion coating film can be provided on the surface of the metal foil, or a coating film of a metal (dissimilar metal) or a non-metal different from the metal constituting the metal foil can be provided. As the dissimilar metal and non-metal, for example, a metal such as titanium or a non-metal such as carbon (conductive carbon, etc.) can be cited.

[0129] The coating film of the above-mentioned dissimilar metal or non-metal (for example, conductive carbon) can also be used as the first layer, and the above-mentioned metal foil can be used as the second layer.

[0130] In the case where the cathode lead-out layer contains a metal particle-containing layer, the entire cathode lead-out layer can be constituted by the metal particle-containing layer, or the first layer can be constituted by the metal particle-containing layer, or the second layer can be constituted by the metal particle-containing layer. For example, the cathode lead-out layer can contain a first layer (carbon layer) containing conductive carbon and a second layer containing a metal particle-containing layer covering at least a part of the first layer.

[0131] The cathode lead-out layer is formed by a known method according to its layer structure. For example, in the case where the cathode lead-out layer includes a metal foil as the first layer or the second layer, the metal foil is laminated so as to cover at least a part of the solid electrolyte layer or the first layer, thereby forming the first layer or the second layer. The first layer containing conductive particles is formed, for example, by applying a conductive paste or a liquid dispersion containing conductive particles and, if necessary, a resin binder (such as a water-soluble resin, a curable resin, etc.) to the surface of the solid electrolyte layer. The second layer containing metal powder is formed, for example, by applying a paste containing metal powder and a resin binder to the surface of the first layer. During the formation of the cathode lead-out layer, drying treatment, heat treatment, etc. can also be carried out as needed.

[0132] (Separator)

[0133] In the case where a metal foil is used for the cathode lead-out layer, a separator can also be disposed between the metal foil and the anode foil. There is no particular limitation on the separator. For example, a non-woven fabric containing fibers of cellulose, polyethylene terephthalate, vinylon, polyamide (such as aliphatic polyamide, aromatic polyamide such as aromatic polyamide), etc. can be used.

[0134] (Others)

[0135] The solid electrolytic capacitor of the present disclosure has high charge and discharge characteristics, and dielectric breakdown when a high voltage is applied is suppressed, showing excellent withstand voltage characteristics. Therefore, the solid electrolytic capacitor of the present disclosure is suitable for high-voltage applications and can ensure a high safety factor of the rated voltage. For example, by setting the average thickness T of the dielectric layer to 2.50×Rv (nm) or more, a safety factor of more than twice the rated voltage can be ensured. The rated voltage Rv of the solid electrolytic capacitor can be 12V or more, or can be 16V or more.

[0136] The solid electrolytic capacitor includes at least one capacitor element. The solid electrolytic capacitor can be of a wound type, or can be any of a chip type or a stacked type. For example, the solid electrolytic capacitor can also include a plurality of stacked capacitor elements. In addition, the solid electrolytic capacitor can also include two or more wound capacitor elements. The structure of the capacitor element can be selected according to the type of the solid electrolytic capacitor.

[0137] In the capacitor element, the cathode lead-out layer is electrically connected to one end of the cathode lead terminal. The cathode lead terminal, for example, coats a conductive adhesive on the cathode lead-out layer and is joined to the cathode lead-out layer by means of the conductive adhesive. The anode foil is electrically connected to one end of the anode lead terminal. The other ends of the anode lead terminal and the cathode lead terminal are respectively led out from the resin package or the housing. The other ends of the respective terminals exposed from the resin package or the housing are used for soldering to the substrate on which the solid electrolytic capacitor should be mounted, etc.

[0138] The capacitor element is sealed using a resin package or a case. For example, the capacitor element and the resin material of the package (e.g., uncured thermosetting resin and filler) can be placed in a mold, and the capacitor element can be sealed with the resin package by transfer molding, compression molding, etc. At this time, the anode lead terminal connected to the anode lead drawn from the capacitor element and the part on the other end side of the cathode lead terminal are respectively exposed from the mold. Alternatively, the capacitor element can be placed in a bottomed case with the part on the other end side of the anode lead terminal and the cathode lead terminal located on the opening side of the bottomed case, and the opening of the bottomed case can be sealed with a sealing body to form a solid electrolytic capacitor.

[0139] Figure 1 It is a cross-sectional view schematically showing the structure of a solid electrolytic capacitor according to an embodiment of the present disclosure. As Figure 1 shown, the solid electrolytic capacitor 1 includes a capacitor element 2, a resin package 3 that seals the capacitor element 2, and an anode lead terminal 4 and a cathode lead terminal 5, at least a part of which is respectively exposed to the outside of the resin package 3. The anode lead terminal 4 and the cathode lead terminal 5 can be made of a metal such as copper or a copper alloy, for example. The resin package 3 has a substantially rectangular parallelepiped shape, and the solid electrolytic capacitor 1 also has a substantially rectangular parallelepiped shape.

[0140] The capacitor element 2 includes an anode foil 6 formed of aluminum foil, a dielectric layer 7 covering the anode foil 6, and a cathode portion 8 covering the dielectric layer 7. The cathode portion 8 includes a solid electrolyte layer 9 covering the dielectric layer 7 and a cathode lead layer 10 covering the solid electrolyte layer 9. The anode foil 6 has porous portions formed by etching or the like on both surface layers. In the Raman spectrum of the surface layer of the solid electrolyte layer 9, a peak characteristic of a first polymer component containing a conjugated polymer is observed. The average thickness T of the dielectric layer 7 is 2.50×Rv (nm) or more.

[0141] The anode foil 6 includes a region facing the cathode portion 8 and a region not facing it. In the part of the region of the anode foil 6 that does not face the cathode portion 8 and is adjacent to the cathode portion 8, an insulating separation portion 13 is formed to cover the surface of the anode foil 6 in a strip shape, restricting the contact between the cathode portion 8 and the anode foil 6. Another part of the region of the anode foil 6 that does not face the cathode portion 8 is electrically connected to the anode lead terminal 4 by welding. The cathode lead terminal 5 is electrically connected to the cathode portion 8 by means of an adhesive layer 14 formed of a conductive adhesive.

[0142] [Examples]

[0143] Hereinafter, the present invention will be specifically described based on examples and comparative examples, but the present invention is not limited to the following examples.

[0144] "Solid Electrolytic Capacitors A1 to A2 and R1"

[0145] Manufacture is carried out according to the following procedures Figure 1 The solid electrolytic capacitor 1 (solid electrolytic capacitors A1, A2, and R1) shown in the figure is manufactured, and its characteristics are evaluated.

[0146] (1) Preparation of the anode foil 6

[0147] The two surfaces of an aluminum foil (thickness: 130 μm) are roughened by etching to fabricate the anode foil 6. The thicknesses of the porous portions formed on the two surface layers of the anode foil are 50 μm each.

[0148] (2) Formation of the dielectric layer 7

[0149] The cathode forming portion of the anode foil 6 is immersed in a chemical conversion solution maintained at 70 °C, and a DC voltage of the value shown in Table 2 is applied to form the dielectric layer 7 containing alumina. As the chemical conversion solution, an aqueous solution of ammonium adipate with a concentration of 0.3 mass% is used. The voltage applied during chemical conversion is adjusted according to the rated voltage Rv so that the average thickness T of the dielectric layer 7 and the rated voltage Rv of the solid electrolytic capacitor have the relationship shown in Table 2. In addition, the voltage application time is 25 minutes to 35 minutes.

[0150] (3) Formation of the solid electrolyte layer 9

[0151] An insulating resistive tape is pasted between the region where the solid electrolyte layer 9 is to be formed and the region where the solid electrolyte layer 9 is not formed on the anode foil 6 on which the dielectric layer 7 has been formed, thereby forming the separation portion 13. The anode foil 6 on which the separation portion 13 has been formed is immersed in a liquid composition containing a conductive material, taken out and dried, thereby forming a pre-coating (not shown).

[0152] EDOT monomer and PSS (Mw: 100,000) as a polymeric anion are dissolved in ion-exchanged water to prepare a mixed solution. While stirring the mixed solution, iron sulfate (oxidizing agent) dissolved in ion-exchanged water is added to prepare a polymerization solution. Using the obtained polymerization solution, electrolytic polymerization is carried out in a three-electrode system. More specifically, the anode foil 6 on which the pre-coating has been formed, a counter electrode, and a reference electrode (silver / silver chloride reference electrode) are immersed in the polymerization solution. A voltage is applied to the anode foil 6 so that the potential of the anode foil 6 with respect to the reference electrode (polymerization voltage) becomes 1.0 V, and electrolytic polymerization is carried out at 25 °C to form the solid electrolyte layer 9.

[0153] (4) Formation of the cathode lead-out layer 10

[0154] The anode foil 6 obtained in the process of (3) above is immersed in a dispersion liquid in which graphite particles are dispersed in water, taken out from the dispersion liquid, and dried, thereby forming at least the first layer (carbon layer) 11 on the surface of the solid electrolyte layer 9. The drying is carried out at 130 to 180 °C for 10 to 30 minutes.

[0155] Next, a silver paste containing silver particles and a binder resin (epoxy resin) is coated on the surface of the first layer 11 and heated at 150 to 200 °C for 10 to 60 minutes, thereby curing the binder resin and forming the second layer (metal particle-containing layer) 12. In this way, the cathode lead-out layer 10 composed of the first layer (carbon layer) 11 and the second layer (metal particle-containing layer) 12 is formed, and the cathode portion 8 composed of the solid electrolyte layer 9 and the cathode lead-out layer 10 is formed.

[0156] As described above, the capacitor element 2 is manufactured.

[0157] (5) Assembly of the solid electrolytic capacitor

[0158] The cathode portion 8 of the capacitor element 2 obtained in (4) above is joined to one end portion of the cathode lead terminal 5 by the adhesive layer 14 of the conductive adhesive. One end portion of the anode foil 6 protruding from the capacitor element 2 is joined to one end portion of the anode lead terminal 4 by laser welding.

[0159] Next, by molding, a resin outer package 3 formed of an insulating resin is formed around the capacitor element 2. At this time, the other end portions of the anode lead terminal 4 and the cathode lead terminal 5 are in a state of being led out from the resin outer package 3.

[0160] In this way, the solid electrolytic capacitor 1 (A1, A2, and B1) with a rated voltage Rv of 20V is completed. A total of 20 solid electrolytic capacitors are manufactured in the same manner as above.

[0161] 《Solid electrolytic capacitor B1》

[0162] The solid electrolyte layer 9 is formed according to the following steps. Except for this, the solid electrolytic capacitor is manufactured in the same manner as in the case of the solid electrolytic capacitor A1.

[0163] The anode foil 6 having the dielectric layer 7 is immersed in a liquid dispersion containing a conductive polymer and dried at 120 °C for 10 to 30 minutes. Further, the immersion and drying in the liquid dispersion are each repeated 4 times, thereby forming the solid electrolyte layer 9. As the liquid dispersion, an aqueous dispersion liquid containing PEDOT and PSS (Mw = 160000) at a concentration of 2 to 4 mass% (average particle diameter of the conductive polymer in the dispersion liquid: 400 nm to 600 nm) is used.

[0164] [Evaluation]

[0165] Using solid electrolytic capacitors, the following evaluations were conducted.

[0166] (a) Raman spectroscopy measurement of the solid electrolyte layer

[0167] Using solid electrolytic capacitors, the Raman spectrum of the cross-section of the solid electrolyte layer was measured according to the described procedure. In the Raman spectra of the surface layer and the first part of the solid electrolyte layer of solid electrolytic capacitors A1 to A2, a peak (first peak) characteristic of the 5-membered ring of PEDOT was observed at a wavenumber near 1420 cm -1 , and a peak (second peak) characteristic of the aromatic ring - S element bond of PSS was observed at a wavenumber near 1000 cm -1 . For the first part of the solid electrolyte layer, the intensity I p1 of the first peak and the intensity I p2 of the second peak were obtained, and the ratio I p1 / I p2 was calculated.

[0168] (b) Presence ratio of S element in the porous part

[0169] Using solid electrolytic capacitors, according to the described procedure, EPMA analysis was performed on the cross-section of the porous part of the anode foil 6, and the Net intensities of the Al element and the S element were obtained from the elemental mapping. The presence ratio of the S element was obtained from the Net intensities of these elements according to the described procedure.

[0170] (c) Capacitance

[0171] In an environment of 20°C, using an LCR meter for 4-terminal measurement, the initial capacitance (μF) at a frequency of 120 Hz of each solid electrolytic capacitor was measured. Then, the average value (C0) of 20 solid electrolytic capacitors was obtained.

[0172] Next, at a temperature of 70°C, the solid electrolytic capacitor was charged at the rated voltage for 30 seconds and discharged at the rated voltage for 30 seconds. More specifically, according to the curve shown in Table 1 below, the charging and discharging in the first cycle and the charging and discharging in the second cycle were repeatedly performed in sequence up to 10,000 cycles. Then, in the same manner as in the case of the initial capacitance, the capacitance was measured in a 20°C environment, and the average value (C1) of 20 solid electrolytic capacitors was obtained. The capacitance change rate (ΔC) was obtained from the following formula.

[0173] Capacitance change rate (ΔC): (C1 - C0) / C0 × 100 (%)

[0174] The capacitance change rate is negative, and the smaller it is, the more the capacity decreases after repeated charging and discharging.

[0175] [Table 1]

[0176]

[0177] (d) Dielectric breakdown voltage

[0178] At a temperature of 70°C, a voltage is applied to the solid electrolytic capacitor while increasing the voltage at a rate of 1.0 V / second, and the dielectric breakdown voltage (V) at which an overcurrent of 0.5 A flows is measured.

[0179] The evaluation results are shown in Table 2. Solid electrolytic capacitors A1 and A2 are examples, solid electrolytic capacitor R1 is a reference example, and solid electrolytic capacitor B1 is a comparative example. Regarding the initial capacitance C0 and the initial ESR, the relative values are expressed when the value of solid electrolytic capacitor B1 is set to 100.

[0180] [Table 2]

[0181]

[0182] As shown in Table 2, in solid electrolytic capacitor R1, since the solid electrolyte layer is formed by three - electrode electrolytic polymerization, a high initial capacitance is obtained, and the capacitance change rate ΔC during repeated charge and discharge is also suppressed to a low level. However, since the average thickness of the dielectric layer is 2.5 Rv or less, the dielectric breakdown voltage is low. In solid electrolytic capacitor B1 in which the solid electrolyte layer is formed using a liquid dispersion, the dielectric breakdown voltage is high, but the capacitance decreases significantly during repeated charge and discharge. In contrast, compared with solid electrolytic capacitor B1, solid electrolytic capacitors A1 and A2 have a slightly lower initial capacitance, but the capacitance hardly changes during repeated charge and discharge. Moreover, in solid electrolytic capacitors A1 and A2, a higher dielectric breakdown voltage is obtained compared with solid electrolytic capacitor R1.

[0183] It should be noted that in solid electrolytic capacitor B1, no characteristic peak was measured on the surface layer of the solid electrolyte layer, so the I p1 / I p2 ratio could not be obtained, similar to the situation in the first part. In solid electrolytic capacitors A1 and A2, segregation of polymer anions is suppressed on the surface layer of the solid electrolyte layer in the same manner as in the first part, and the Ip1 / Ip2 ratio is at approximately the same level as in the first part.

[0184] Industrial applicability

[0185] According to the present disclosure, high charge - discharge characteristics are ensured and a high dielectric breakdown voltage is obtained. The solid electrolytic capacitor of the present disclosure stably obtains a high capacitance even during repeated charge and discharge, and has a relatively high dielectric breakdown voltage, so it can be used for various applications requiring high dielectric breakdown voltage, reliability, or long life. However, the uses of solid electrolytic capacitors are not limited to these.

[0186] Description of Reference Numerals

[0187] 1: Solid electrolytic capacitor

[0188] 2: Capacitor element

[0189] 3: Resin outer package

[0190] 4: Anode lead terminal

[0191] 5: Cathode lead terminal

[0192] 6: Anode foil

[0193] 7: Dielectric layer

[0194] 8: Cathode portion

[0195] 9: Solid electrolyte layer

[0196] 10: Cathode lead-out layer

[0197] 11: First layer (carbon layer)

[0198] 12: Second layer (layer containing metal particles)

[0199] 13: Separation layer

[0200] 14: Adhesive layer

Claims

1. A solid electrolytic capacitor comprising at least one capacitor element, wherein the capacitor element comprises: an anode foil having a porous portion at least on a surface layer; a dielectric layer covering at least a part of the anode foil; and a solid electrolyte layer covering at least a part of the dielectric layer, wherein the solid electrolyte layer comprises a first polymer component containing a conjugated polymer and a second polymer component containing a polymer anion, in a Raman spectrum of a surface layer of the solid electrolyte layer, a peak peculiar to the first polymer component is observed, when the rated voltage of the solid electrolytic capacitor is set to Rv (V), an average thickness T of the dielectric layer is 2.50×Rv (nm) or more.

2. The solid electrolytic capacitor according to claim 1, wherein, The solid electrolyte layer contains sulfur element, The anode foil contains aluminum element, the solid electrolyte layer has: a first portion filled in pores of the porous portion of the anode foil having the dielectric layer and a second portion disposed outside the anode foil having the dielectric layer and closer to the main surface of the anode foil having the dielectric layer, in an element mapping obtained by an electron probe microanalyzer of a cross section of the porous portion, when the presence ratio of aluminum element in the porous portion is set to 100%, the presence ratio of sulfur element in the porous portion is 0.5% or more.

3. The solid electrolytic capacitor according to claim 1 or 2, wherein, The average thickness T of the dielectric layer is 3.5×Rv (nm) or less.

4. The solid electrolytic capacitor according to claim 1 or 2, wherein, The rated voltage Rv is 12 V or more.

5. The solid electrolytic capacitor according to claim 1 or 2, wherein, The conjugated polymer contains a monomer unit corresponding to a thiophene compound.

6. The solid electrolytic capacitor according to claim 5, wherein, The peak characteristic of the first polymer component is the first peak observed in a wavenumber range above 1200 cm -1 and below 1600 cm -1 .

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

8. The solid electrolytic capacitor according to claim 1 or 2, wherein The weight average molecular weight of the polymer anion is 100 or more and 500,000 or less.

9. The solid electrolytic capacitor according to claim 1 or 2, wherein, The polymer anion contains a monomer unit corresponding to an organic sulfonic acid compound.

10. The solid electrolytic capacitor according to claim 1 or 2, wherein, The peak characteristic of the first polymer component is a first peak observed in a wavenumber range of above 1200 cm -1 and below 1600 cm -1 . The polymer anion contains a monomer unit corresponding to an aromatic sulfonic acid compound, In the Raman spectrum of the surface layer of the solid electrolyte layer, a second peak characteristic of the observed second polymer component is observed in the wavenumber range above 800 cm -1 and below 1100 cm -1 ​ The intensity I of the first peak p1 relative to the intensity I of the second peak p2 The ratio (= I p1 / I p2 ) is 2 or more.

11. The solid electrolytic capacitor according to claim 2, wherein, In the Raman spectrum of the first part, the intensity I of the first peak characteristic of the first polymer component p1 relative to the intensity I of the second peak characteristic of the second polymer component p2 The ratio (= I p1 / I p2 ) is 2 or more.

12. The solid electrolytic capacitor according to claim 1 or 2, comprising the capacitor element and a plurality of capacitor elements stacked on each other.

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