Electrolytic capacitor and method for manufacturing the same

Abstract

To provide an electrolytic capacitor and a method for manufacturing the electrolytic capacitor, the electrolytic capacitor being capable of favorably suppressing leakage current by using plastic crystal.SOLUTION: The method for manufacturing an electrolytic capacitor includes a plastic-crystal attaching step of attaching a plastic crystal. The plastic-crystal attaching step includes: a melting process of heating the plastic crystal to a temperature equal to or higher than a melting temperature to form a molten salt; a molten-salt impregnation process of impregnating an element in which a conductive polymer is interposed between an anode body and a cathode body, with the molten salt; and a crystallization step of returning the molten salt impregnated in the element to the plastic crystal. The plastic crystal is contained in the bottom of the etching pit in an amount of at least 75%, on the basis of the content at the opening position of the etching pit.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an electrolytic capacitor and a manufacturing method thereof. [Background technology]

[0002] Electrolytic capacitors use valve metals such as tantalum or aluminum as anode and cathode foils. The anode foil is enlarged by forming a powder sintered layer made of valve metal powder on the foil surface, or by etching the foil itself. The enlarged surface has a dielectric coating. An electrolyte is interposed between the anode and cathode foils. The electrolyte is in close contact with the uneven surface of the anode foil and functions as the true cathode.

[0003] Capacitors are used in a variety of applications. In all applications, there is a growing demand for higher capacitance. In this regard, electrolytic capacitors have the advantage that the specific surface area can be increased by expanding the surface of the anode foil, making it easier to obtain a large capacitance compared to other types of capacitors such as film capacitors. Furthermore, electrolytic capacitors contain electrolyte in the form of an electrolytic solution. The contact area of the electrolytic solution with the dielectric film on the anode foil increases. This makes it easier to further increase the capacitance of electrolytic capacitors.

[0004] In recent years, solid electrolytic capacitors using a solid electrolyte as the electrolyte have become widespread (see, for example, Patent Document 1). Because electrolytic capacitors use a highly conductive solid electrolyte, they are small in size, have large capacity, and also have low equivalent series resistance (low ESR). Furthermore, in addition to being small in size, having large capacity, and having low ESR, electrolytic capacitors using a solid electrolyte as the electrolyte have other characteristics, such as being easy to fabricate into chips and being suitable for surface mounting, making them essential for miniaturizing, improving functionality, and reducing the cost of electronic devices.

[0005] Known examples of solid electrolytes include manganese dioxide and 7,7,8,8-tetracyanoquinodimethane (TCNQ) complexes. In recent years, conductive polymers have rapidly become popular as solid electrolytes. Conductive polymers are derived from monomers with π-conjugated double bonds, such as poly(3,4-ethylenedioxythiophene) (PEDOT). PEDOT has a slow reaction rate and excellent adhesion to dielectric films. Conductive polymers use acid compounds such as polyanions as dopants, and the monomer molecules contain substructures that act as dopants, resulting in high conductivity and promoting low ESR in electrolytic capacitors. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2007 / 091656 Summary of the Invention [Problem to be solved by the invention]

[0007] However, solid electrolytes have poor repair properties for defects in the dielectric film, which can lead to increased leakage current. So-called hybrid electrolytic capacitors have been proposed, in which the voids in the capacitor element are impregnated with an electrolytic solution or an ionic liquid. However, even solid electrolytes are desired to have the ability to suppress leakage current.

[0008] The present invention has been proposed to solve the above problems, and its object is to provide an electrolytic capacitor that can effectively suppress leakage current by using a plastic crystal, and a manufacturing method thereof. [Means for solving the problem]

[0009] In order to solve the above-described problems, the method for manufacturing an electrolytic capacitor of this embodiment includes an element forming step of forming an element including an anode body and a cathode body each having a dielectric film, a solid electrolyte attaching step of attaching a solid electrolyte to the anode body, and a plastic crystal attaching step of further attaching a plastic crystal to the anode body, the plastic crystal attaching step including a melting step of heating the plastic crystal to a melting temperature or higher to form a molten salt, a molten salt impregnation step of impregnating the element with the solid electrolyte attached thereto with the molten salt, and a crystallization step of returning the molten salt impregnated into the element to form the plastic crystal.

[0010] This allows the plastic crystals to be contained in the bottom of the etching pit at 75% or more, based on the content at the opening of the etching pit. In other words, the plastic crystals can also act on defects that occur at the bottom of the etching pit, effectively suppressing leakage current in electrolytic capacitors.

[0011] The melting temperature of the plastic crystal may be set to be higher than the capacitor's guaranteed temperature. That is, it is preferable to use a plastic crystal that does not melt during operation of the electrolytic capacitor except during the manufacturing process of the electrolytic capacitor. This prevents the plastic crystal from scattering outside the capacitor when the valve is opened.

[0012] The melting temperature of the plastic crystals may be greater than 150°C.

[0013] After the plastic crystal attachment step, a voltage application step of applying a voltage to the element may be performed.

[0014] In order to solve the above-mentioned problems, the electrolytic capacitor of this embodiment includes an anode body having a dielectric film and an etching pit, a cathode body facing the anode body, and an electrolyte layer including a solid electrolyte and a plastic crystal, and the plastic crystal is contained in an amount of 75% or more at the bottom of the etching pit, based on the content at the opening position of the etching pit.

[0015] This increases the probability that the plastic crystals will also act on defective areas occurring at the bottom of the etching pit, effectively suppressing leakage current from the electrolytic capacitor. [Effects of the Invention]

[0016] According to the present invention, leakage current can be effectively suppressed by using a conductive polymer and a plastic crystal in combination. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 2 is a cross-sectional schematic view of an etching pit. [Figure 2] 1 is a flowchart showing a manufacturing process of an electrolytic capacitor. [Figure 3] 1 is a graph showing the results of EDX analysis, illustrating the boron element content for each depth zone in etching pits in Example 1 and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the embodiments described below.

[0019] (composition) An electrolytic capacitor is a passive device that obtains capacitance through the dielectric polarization of a dielectric film and stores and discharges electric charge. An electrolytic capacitor has a pair of electrodes and an electrolyte layer sandwiched between the electrodes. One electrode is an anode body, and the other electrode is a cathode body.

[0020] The anode body is composed of a valve metal foil and a dielectric coating. A surface-expanding layer is formed on the surface of the foil. The surface-expanding layer can be an etching layer formed by etching the foil, a sintered layer formed by sintering valve metal powder, or a vapor-deposited layer formed by vapor-depositing valve metal particles onto the foil. In other words, the surface-expanding layer has a porous structure, consisting of tunnel-shaped pits, spongy pits, or voids between densely packed powder or particles. This surface-expanding layer is chemically converted to form a dielectric coating on the surface of the foil.

[0021] The electrolyte layer is interposed between the anode body and the cathode body. In other words, the anode body and the cathode body are disposed opposite each other with the electrolyte layer sandwiched between them. The electrolyte layer contains a conductive polymer. The conductive polymer is in close contact with the dielectric film of the anode body and is disposed so as to be continuous between the dielectric film and the cathode body, thereby creating a conductive path and functioning as a true cathode.

[0022] Conductive polymers are self-doped conjugated polymers doped with intramolecular dopant molecules, or conjugated polymers 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. The dopant or external dopant molecule acts as an acceptor that readily accepts electrons into the conjugated polymer, or as a donor that readily donates electrons, which allows the conductive polymer to exhibit high conductivity.

[0023] The electrolyte layer further contains plastic crystals. Plastic crystals, also known as plastic crystals, have an ordered arrangement and a disordered orientation. That is, plastic crystals have a three-dimensional crystal lattice structure in which anions and cations are regularly arranged, while these anions and cations have rotational disorder. The types of anion and cation components that make up the plastic crystals are not particularly limited, as long as they are solid, not ionic liquid, within the target temperature range in which the electrolytic capacitor is used.

[0024] The plastic crystal may be an ionic organic material that has a confirmed solid-phase / solid-phase transition point, has ionic conductivity, and is solid at room temperature. The solid-phase / solid-phase transition point is an endothermic peak that occurs below the melting point during the temperature rise process in differential scanning calorimetry (DSC), i.e., a peak where the value of heat flow per unit weight is negative. On the lower temperature side than this solid-phase / solid-phase transition point, the material has a regular crystalline structure with regular molecular orientation and center of gravity position, and in the range higher than this solid-phase / solid-phase transition point and lower than the melting point, the material is in a plastic crystalline phase. The plastic crystal undergoes a phase transition to a plastic crystalline phase in the room temperature range. In other words, the plastic crystal has a melting point higher than room temperature and a solid-phase / solid-phase transition point lower than room temperature.

[0025] Figure 1 is a cross-sectional schematic diagram of the surface-expanding layer. Note that the dielectric film and electrolyte layer are omitted in Figure 1. As shown in Figure 1, the etching pit is divided into three equal parts in the depth direction: the opening position, the middle position, and the bottom position. In this case, the plastic crystals are contained at 75% or more at the bottom of the etching pit, based on the content at the opening position of the etching pit. The content can be determined by performing energy dispersive X-ray analysis of the cross section of the anode body and measuring the ratio of elements derived from the plastic crystals.

[0026] When the content of plastic crystals at the bottom of the etching pit is 75% or more of the content at the opening position of the etching pit 1, both the initial leakage current and the leakage current after exposure to a high-temperature environment are significantly reduced. "Initial" refers to before the electrolytic capacitor is exposed to a high-temperature environment, and "high-temperature environment" refers to an environment of 150°C or higher. Furthermore, when the content of plastic crystals at the bottom of the etching pit is 75% or more of the content at the opening position of the etching pit, the initial capacitance and the capacitance after exposure to a high-temperature environment are improved.

[0027] When this electrolytic capacitor is subjected to a voltage application process, the leakage current is significantly reduced. Therefore, by incorporating 75% or more of the plastic crystals in the bottom of the etching pit, based on the content at the opening position of the etching pit, the probability that the plastic crystals can act on the defects that occur at the bottom of the etching pit increases, and it is believed that the leakage current of the electrolytic capacitor is effectively suppressed.

[0028] Such electrolytic capacitors include a wound type in which anode bodies and cathode bodies are alternately stacked with a separator sandwiched between them and wound, and a stacked type in which anode bodies and cathode bodies are alternately stacked with a separator sandwiched between them. Alternatively, the electrolytic capacitor may be a flat-plate type in which an electrolyte layer is formed on an individual anode body, and then a carbon layer and a silver layer that become the cathode body are formed on the electrolyte layer.

[0029] (Manufacturing method) Such an electrolytic capacitor, in particular one in which the content of plastic crystals at the bottom of the etching pit is 75% or more of the content at the opening of the etching pit 1, is manufactured as follows. Figure 2 is a flowchart showing the manufacturing process of this electrolytic capacitor. As shown in Figure 2, the manufacturing process of this electrolytic capacitor includes an anode processing step, a cathode processing step, an element forming step, a solid electrolyte attachment step, a sealing body attachment step, a plastic crystal attachment step, and a finishing step.

[0030] (Flexible crystal adhesion process) Among these, the plastic crystal attachment step is a step of housing the element in an exterior case and attaching plastic crystals to the interior of the element. This plastic crystal attachment step includes a melting step, a molten salt impregnation step, and a crystallization step, and by performing these steps in this order, plastic crystals are attached to the interior of the element. Here, the element is composed of an anode body, a cathode body, and an electrolyte layer containing a conductive polymer, with the anode body and the cathode body facing each other with the electrolyte layer sandwiched between them. The element is completed before the plastic crystal attachment step. The exterior case is a container made of aluminum, an aluminum alloy containing aluminum and manganese, or stainless steel, and has one end closed at the bottom and the other open at the end. The opening is sealed with a sealing body after the plastic crystal attachment step.

[0031] In the melting process, the plastic crystals are heated above their melting temperature to form a molten salt. That is, the plastic crystals are heated to a molten state. The melting temperature exceeds the guaranteed temperature of the electrolytic capacitor. In other words, plastic crystals having a melting temperature exceeding the guaranteed temperature of the electrolytic capacitor are included in the electrolyte layer. The guaranteed temperature of the electrolytic capacitor is 150°C or less. That is, plastic crystals having a melting temperature exceeding 150°C are included in the electrolyte layer. At least plastic crystals having a melting temperature higher than the temperature inside the electrolytic capacitor increased by the aging treatment are selected to prevent the plastic crystals from melting during the aging treatment.

[0032] This melting step can be carried out inside an outer case. First, the plastic crystals are dissolved in a solvent in which the plastic crystals are soluble. The solvent is preferably a polar solvent. Examples of polar solvents include acetonitrile, propylene carbonate, γ-butyrolactone, dimethyl carbonate, ethyl methyl carbonate, ethylene carbonate, sulfolane, acetone, methanol, ethanol, isopropyl alcohol, and mixtures thereof. These polar solvents efficiently dissolve the plastic crystals, resulting in excellent productivity for the electrolyte layer. Next, the dissolved plastic crystals are poured into an outer case, and the outer case is heated to volatilize the solvent and melt the plastic crystals.

[0033] In the molten salt impregnation step, the element is placed in an outer case containing molten salt obtained by melting the plastic crystals. The element is partially or entirely immersed in the molten salt inside the outer case. In this way, in the molten salt impregnation step, the molten salt obtained by melting the plastic crystals is impregnated into the element. The element may be depressurized, the molten salt may be pressurized, or both may be used in combination to impregnate the molten salt. The impregnation time is also not particularly limited.

[0034] Then, in the crystallization process, the molten salt impregnated in the element is cooled and converted back into plastic crystals within the element. There are no limitations on the cooling method, and for example, the element impregnated with the molten salt may be left in a room temperature environment. The cooling method may be natural cooling or forced air cooling. The cooling temperature is not particularly limited as long as it is maintained at a temperature lower than the melting point of the plastic crystals, and the plastic crystals inside the wound body are transformed from molten salt to crystals. There are also no particular limitations on the cooling time, as long as the plastic crystals are transformed from molten salt to crystals inside the wound body.

[0035] By melting the plastic crystals in this way, the plastic crystals are impregnated into the fine details of the element. Specifically, the plastic crystals can be contained in the bottom of the etching pit at 75% or more of the content at the opening of the etching pit. This significantly reduces both the initial leakage current of the electrolytic capacitor and the leakage current after exposure to a high-temperature environment, and further improves the initial capacitance and the capacitance after exposure to a high-temperature environment.

[0036] The plastic crystal may be an ionic organic substance having a solid-solid transition point, ionic conductivity, and a melting point lower than room temperature. Furthermore, the solid-solid transition point is lower than the operating temperature range of the electrolytic capacitor, and the melting point is higher than the operating temperature range of the electrolytic capacitor. The operating temperature range of the electrolytic capacitor is between -40°C and 150°C when it is intended for outdoor use, such as in a vehicle.

[0037] The solid-solid phase transition point is an endothermic peak that occurs below the melting point during the temperature rise process in differential scanning calorimetry (DSC), i.e., a peak where the heat flow per unit weight is negative. Below this solid-solid phase transition point, the material has a regular crystalline structure with regular molecular orientation and center of gravity. Above this solid-solid phase transition point and below the melting point, the material is in a plastic crystalline phase. The plastic crystalline phase transitions to a plastic crystalline phase at room temperature. Therefore, this electrolytic capacitor operates while maintaining the ionic organic material, which has a melting point higher than room temperature and a solid-solid phase transition point lower than room temperature, in a plastic crystalline state.

[0038] In addition, any known type of plastic crystal can be used as long as its melting point exceeds the guaranteed temperature of the electrolytic capacitor or it does not dissolve during aging treatment. Examples of anion components constituting the plastic crystal include various amide anions, tris(trifluoromethanesulfonyl)methanide anions, various phosphate anions, various borate anions, various sulfone-based anions, and tetrafluoroaluminate anions.

[0039] In the various amide anions, two hydrogen atoms of the NH anion are substituted with perfluoroalkylsulfonyl groups, fluorosulfonyl groups, or both. The various amide anions include, for example, linear anions, such as various bis(perfluoroalkylsulfonyl)amide anions, bis(fluorosulfonyl)amide anions, and various N-(fluorosulfonyl)-N-(perfluoroalkylsulfonyl)amide anions represented by the following chemical formula (1).

[0040] (chemical 1) TIFF2025121318000002.tif30161In chemical formula (1), n and m are integers of 0 or more, and the number of carbon atoms may be any number.

[0041] In the chemical formula (1), if n and m are 1 or more, the anion is a bis(perfluoroalkylsulfonyl)amide anion. Specific examples of the bis(perfluoroalkylsulfonyl)amide anion include the bis(trifluoromethanesulfonyl)amide anion (TFSA anion) represented by the following chemical formula (2) and the bis(pentafluoroethylsulfonyl)amide anion (BETA anion) represented by the following chemical formula (3).

[0042] (Case 2) TIFF2025121318000003.tif37161

[0043] (3) TIFF2025121318000004.tif38161

[0044] Specific examples of the bis(perfluoroalkylsulfonyl)amide anion include (pentafluoroethylsulfonyl)trifluoromethanesulfonylamide anion, which is represented by the following chemical formula (4) in which n is 1 and m is 2 in the chemical formula (1).

[0045] (C4) TIFF2025121318000005.tif41161

[0046] In chemical formula (1), a group having 0 carbon atoms is a fluorosulfonyl group, and when n and m are 0, the anion is a bis(fluorosulfonyl)amide anion (FSA anion) represented by the following chemical formula (5).

[0047] (C5) TIFF2025121318000006.tif37161

[0048] In the chemical formula (1), when n is 0 and m is 1 or more, the anion is an N-(fluorosulfonyl)-N-(perfluoroalkylsulfonyl)amide anion represented by the following chemical formula (6). Specific examples of the N-(fluorosulfonyl)-N-(perfluoroalkylsulfonyl)amide anion include the N-(fluorosulfonyl)-N-(trifluoromethanesulfonyl)amide anion represented by the following chemical formula (7) when m is 1, and the N-(fluorosulfonyl)-N-(pentafluoroethylsulfonyl)amide anion represented by the following chemical formula (8) when m is 2.

[0049] (6) TIFF2025121318000007.tif35161

[0050] (C7) TIFF2025121318000008.tif41161

[0051] (8) TIFF2025121318000009.tif41161

[0052] The various amide anions also include a (perfluoroalkylsulfonyl)fluoroacetamide anion, which is represented by the following chemical formula (9) and in which two hydrogen atoms of the NH2 anion are substituted with a perfluoroalkylsulfonyl group and a fluoroacetyl group. (9) TIFF2025121318000010.tif41164In chemical formula (9), n is an integer of 0 or more, and the number of carbon atoms may be any number.

[0053] Furthermore, various amide anions include, for example, five-membered and six-membered heterocyclic rings, such as N,N-hexafluoro-1,3-disulfonylamide anion (CFSA anion) represented by the following chemical formula (10) and N,N-pentafluoro-1,3-disulfonylamide anion represented by the following chemical formula (11).

[0054] (C10) TIFF2025121318000011.tif56161

[0055] (Chem.11) TIFF2025121318000012.tif51161

[0056] The tris(trifluoromethanesulfonyl)methanide anion (TFSM anion) is represented by the following chemical formula (12). (C12) TIFF2025121318000013.tif64161

[0057] The various phosphate anions are hexafluorophosphate anions (PF6 anions) represented by the following chemical formula (13), or various perfluoroalkylphosphate anions represented by the following chemical formula (14), in which some of the fluorine atoms of PF6 are substituted with fluoroalkyl groups.

[0058] (C13) TIFF2025121318000014.tif38161

[0059] (C14) TIFF2025121318000015.tif38161In chemical formula (14), q is an integer of 1 or more, and the number of carbon atoms may be any number.

[0060] Specifically, tris(pentafluoroethyl)trifluorophosphate anion (FAP anion) represented by the following chemical formula (15) can be mentioned. (C15) TIFF2025121318000016.tif48161

[0061] Examples of the various borate anions include tetrafluoroborate anion (BF4 anion) represented by the following chemical formula (16), and various perfluoroalkylborate anions represented by the following chemical formula (17) in which some of the fluorine atoms in the BF4 anion are substituted with fluoroalkyl groups. Specific examples of the various perfluoroalkylborate anions include mono(fluoroalkyl)trifluoroborate anion and bis(fluoroalkyl)fluoroborate anion.

[0062] (C16) TIFF2025121318000017.tif39161

[0063] (C17) TIFF2025121318000018.tif39161In the formula, s is an integer of 0 or more, t is an integer of 1 or more, and the number of carbon atoms may be any number.

[0064] Furthermore, the various borate anions further include a borate anion represented by the following chemical formula (18). (C18) TIFF2025121318000019.tif29161In the formula, R1 and R2 are each independently a ketone group, or R1 and R2 are carbon atoms in a common six-membered aromatic ring.In the formula, R3 and R4 are each independently a ketone group, or R3 and R4 are carbon atoms in a common six-membered aromatic ring.

[0065] In the chemical formula (18), when R1, R2, R3, and R4 are all ketone groups, the anion is a bis(oxalato)borate (BoB) anion represented by the following chemical formula (19). (C19) TIFF2025121318000020.tif42161

[0066] Furthermore, in chemical formula (18), if R1 and R2 are carbon atoms that form a common six-membered aromatic ring, and R3 and R4 are carbon atoms that form a common six-membered aromatic ring, then the anion is a bis(pyrocatecholato)borate anion represented by the following chemical formula (20). (20) TIFF2025121318000021.tif29161

[0067] Furthermore, the various borate anions further include a borate anion represented by the following chemical formula (21). (21) TIFF2025121318000022.tif32161In the formula, R1 to R6 are each independently a ketone group or a methylene group. Alternatively, in the formula, either R1 or R3 is a ketone group or a methylene group, and the other combination of R1 and R2 or the other combination of R2 and R3 is a carbon atom of a common six-membered aromatic ring. In the formula, either R4 or R6 is a ketone group or a methylene group, and the other combination of R4 and R5 or the other combination of R5 and R6 is a carbon atom of a common six-membered aromatic ring. The six-membered aromatic ring may have one or four methyl groups, or the six-membered aromatic ring may be part of a polycyclic aromatic ring having two or more aromatic rings, such as a naphthalene ring.

[0068] In the chemical formula (21), if R1 and R6 are ketone groups, R2 and R3 are carbon atoms that form a common six-membered aromatic ring, and R4 and R5 are carbon atoms that form a common six-membered aromatic ring, the anion is a bis(salicylato)borate anion (BScB anion) represented by the following chemical formula (22). (22) TIFF2025121318000023.tif55161

[0069] In the chemical formula (21), when R1 and R6 are ketone groups, R2 and R3 are carbon atoms constituting a common six-membered aromatic ring, R4 and R5 are carbon atoms constituting a common six-membered aromatic ring, and both aromatic six-membered rings each have four methyl groups, the resulting anion is bis(tetramethylsalicylato)borate, as represented by the following chemical formula (23). (23) TIFF2025121318000024.tif58161

[0070] In the chemical formula (21), when R1 and R6 are ketone groups, R2 and R3 are carbon atoms constituting a common six-membered aromatic ring, R4 and R5 are carbon atoms constituting a common six-membered aromatic ring, and both aromatic six-membered rings each have one methyl group, the resulting anion is a bis(methylsalicylate)borate anion (BmScB anion) represented by the following chemical formula (24). (24) TIFF2025121318000025.tif48161

[0071] In the chemical formula (21), when R1 and R6 are ketone groups, R2 and R3 are carbon atoms forming a common naphthalene ring, and R4 and R5 are carbon atoms forming a common naphthalene ring, the anion is a bis(1-hydroxy-2-naphtholato)borate anion represented by the following chemical formula (25), a bis(2-hydroxy-1-naphtholato)borate anion (BhNB anion) represented by the following chemical formula (26), or a bis(3-hydroxy-2-naphtholato)borate anion represented by the following chemical formula (27).

[0072] (25) TIFF2025121318000026.tif68161

[0073] (26) TIFF2025121318000027.tif38161

[0074] (27) TIFF2025121318000028.tif54161

[0075] Examples of various sulfone-based anions include alkylsulfonate anions represented by the following chemical formula (28), various perfluoroalkylsulfonate anions represented by the following chemical formula (29), and p-toluenesulfonate anions represented by the following chemical formula (30).

[0076] (28) TIFF2025121318000029.tif7161In chemical formula (28), x is an integer of 1 or more and 4 or less.

[0077] (C29) TIFF2025121318000030.tif7161In chemical formula (29), y is an integer of 1 or more and 4 or less.

[0078] Specifically, various perfluoroalkylsulfonate anions include a trifluoromethanesulfonate anion in which y is 1 in the above chemical formula (29), a pentafluoroethylsulfonate anion in which y is 2 in the above chemical formula (29), a heptafluoropropanesulfonate anion in which y is 3 in the above chemical formula (29), and a nonafluorobutanesulfonate anion in which y is 4 in the above chemical formula (29).

[0079] (30) TIFF2025121318000031.tif28161

[0080] The tetrafluoroaluminate anion is represented by the following chemical formula (31). (31) TIFF2025121318000032.tif39161

[0081] Examples of cationic components constituting the plastic crystal include various quaternary ammonium cations, various pyrrolidinium cations, various piperidinium cations, various imidazolium cations, various phosphonium cations, and various trialkylsulfonyl cations.

[0082] Examples of the quaternary ammonium cation include tetraalkylammonium cations represented by the following chemical formula (32) and substituted with a linear alkyl group, regardless of the number of carbon atoms. (C32) TIFF2025121318000033.tif47161In the formula, a, b, c, and d are integers of 1 or more, and the number of carbon atoms may be any number.

[0083] In the above chemical formula (32), when a, b, c, and d are 2, it is a tetraethylammonium cation (TEA cation) represented by the following chemical formula (33). (33) TIFF2025121318000034.tif38165

[0084] In the above chemical formula (32), when a, b, and c are 2 and d is 1, it is a triethylmethylammonium cation (TEMA cation) represented by the following chemical formula (34). (34) TIFF2025121318000035.tif38161

[0085] In the above chemical formula (32), when a, b, and c are 1, d is 2, and one of the hydrogen atoms of the ethyl group is substituted with a hydroxy group to form a hydroxyethyl group, the resulting cation is a choline cation (CHL cation) represented by the following chemical formula (35). (35) TIFF2025121318000036.tif32161

[0086] Furthermore, examples of the quaternary ammonium cation include a pyrrolidinium cation represented by the following chemical formula (36), which is a five-membered ring to which a methyl group, an ethyl group, or an isopropyl group is bonded. (36) TIFF2025121318000037.tif46161In the formula, R1 and R2 are methyl groups, ethyl groups, or isopropyl groups.

[0087] Specific examples of the five-membered ring pyrrolidinium cation generalized by the above chemical formula (36) include, for example, the N-ethyl-N-methylpyrrolidinium cation (P12 cation) represented by the following chemical formula (37), the N-isopropyl-N-methylpyrrolidinium cation (P13iso cation) represented by the following chemical formula (38), and the N,N-diethylpyrrolidinium cation (P22 cation) represented by the following chemical formula (39).

[0088] (37) TIFF2025121318000038.tif49161

[0089] (38) TIFF2025121318000039.tif52161

[0090] (39) TIFF2025121318000040.tif48161

[0091] Furthermore, examples of the quaternary ammonium include spiro-pyrrolidinium cations (SBP cations) represented by the following chemical formula (40). (40) TIFF2025121318000041.tif52161

[0092] Various piperidinium cations are represented by the following chemical formula (41), and examples thereof include piperidinium cations in which a methyl group, an ethyl group, or an isopropyl group is a six-membered ring. (C41) TIFF2025121318000042.tif41161In the formula, R3 and R4 are methyl groups, ethyl groups, or isopropyl groups.

[0093] A specific example of the six-membered ring piperidinium cation generalized by the above chemical formula (41) is, for example, the 1-ethyl-1-methylpiperidinium cation represented by the following chemical formula (42), in which R1 is a methyl group and R2 is an ethyl group. (C42) TIFF2025121318000043.tif36161

[0094] The various imidazolium cations are 1,3-dialkylimidazolium or 1,2,3-trialkylimidazolium cations represented by the following chemical formula (43). (C43) TIFF2025121318000044.tif46161In the formula, h and i are integers between 1 and 3, and j is 0 or 1.

[0095] In chemical formula (43), when j is 0, and h and i are 1, the compound is a 1,3-dimethylimidazolium cation (DMI cation) represented by the following chemical formula (44). The 2-position of this DMI cation may be substituted with a methyl group. (C44) TIFF2025121318000045.tif30161

[0096] In chemical formula (43), when j is 0, h is 1, and i is 2, the cation is a 1-ethyl-3-methylimidazolium cation (EMI cation) represented by the following chemical formula (45). The 2-position of this EMI cation may be substituted with a methyl group. (C45) TIFF2025121318000046.tif30161

[0097] In chemical formula (43), when j is 0, h is 1, and i is 3, it is a 1-methyl-3-propylimidazolium cation (MPI cation) represented by the following chemical formula (46). The 2-position of this MPI cation may be substituted with a methyl group. (C46) TIFF2025121318000047.tif30161

[0098] The various phosphonium cations are represented by the following chemical formula (47), and examples thereof include tetraalkylphosphonium cations substituted with a linear alkyl group, regardless of the number of carbon atoms. Examples of the tetraalkylphosphonium cations include tetraethylphosphonium cations (TEP cations). (C47) TIFF2025121318000048.tif47161In the formula, e, f, g, and h are integers of 1 or more, and the number of carbon atoms may be any number.

[0099] Examples of various trialkylsulfonyl cations include the trimethylsulfonium cation represented by the following chemical formula (48), in which all hydrogen atoms of the sulfonium are substituted with methyl groups. (C48) TIFF2025121318000049.tif38161

[0100] Two or more types of plastic crystals may be included in the electrolyte layer. When two or more types of plastic crystals are included, plastic crystals of the same anion type may be included in the electrolyte layer, plastic crystals of the same cation type may be included in the electrolyte layer, or plastic crystals with different anion and cation components may be included in the electrolyte layer. The blending ratio of different plastic crystals in the electrolyte layer may be equimolar or may be different.

[0101] Plastic crystals can be produced, for example, by the following manufacturing method, but various other methods can also be used. Specifically, alkali metal salts of the anion components that make up the plastic crystals and halogenated cation components are each dissolved in a solvent. Examples of alkali metals include Na, K, Li, and Cs. Examples of halogens include F, Cl, Br, and I. Water is preferred as the solvent. An ion exchange reaction is carried out by gradually adding a solution of the metal salt of the anion to the solution of the halogenated cation. An equimolar amount of the solution of the metal salt of the anion is added to the solution of the halogenated cation, and the mixture is stirred.

[0102] At this time, ion exchange produces plastic crystals and alkali metal halides. When an organic solvent such as dichloromethane is mixed and allowed to stand, the mixture separates into an aqueous layer and an organic solvent layer. The alkali metal halides are removed by removing the aqueous layer. This operation can be repeated multiple times. After removing the alkali metal halides, the organic solvent such as dichloromethane is evaporated to obtain plastic crystals.

[0103] The plastic crystals are dissolved in a solvent in which the plastic crystals are soluble. The solvent is preferably a polar solvent. Examples of polar solvents include acetonitrile, propylene carbonate, γ-butyrolactone, dimethyl carbonate, ethyl methyl carbonate, ethylene carbonate, sulfolane, acetone, methanol, ethanol, isopropyl alcohol, and mixtures thereof. These polar solvents efficiently dissolve the plastic crystals, resulting in excellent productivity of the electrolyte layer.

[0104] The object to which the electrolyte layer is to be attached is then impregnated with a solution of plastic crystals. After impregnation with the solution of plastic crystals, the object is left in a temperature environment at which the solvent volatilizes, such as at 100°C, to volatilize the solvent by drying, and then left in a temperature environment at 150°C, etc., to volatilize any remaining moisture. This allows plastic crystals to be formed on the object to be attached.

[0105] The plastic crystal may be doped with an ionic salt that serves as an electrolyte. The ionic salt may be a salt of an organic acid, a salt of an inorganic acid, or a salt of a complex compound of an organic acid and an inorganic acid, and may be used alone or in combination of two or more.

[0106] Examples of organic acids include carboxylic acids such as oxalic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, maleic acid, adipic acid, benzoic acid, toluic acid, enanthic acid, malonic acid, 1,6-decanedicarboxylic acid, 1,7-octanedicarboxylic acid, azelaic acid, undecanedioic acid, dodecanedioic acid, and tridecanedioic acid, as well as phenols and sulfonic acids. Examples of inorganic acids include boric acid including tetrafluoroborate, phosphoric acid, phosphorous acid, hypophosphorous acid, carbonic acid, and silicic acid. Examples of composite compounds of organic and inorganic acids include borodisalicylic acid, borodioxalic acid, and borodiglycolic acid.

[0107] Examples of the salts of these organic acids, inorganic acids, and at least one salt of a complex compound of an organic acid and an inorganic acid include ammonium salts, quaternary ammonium salts, quaternized amidinium salts, amine salts, sodium salts, and potassium salts. Examples of the quaternary ammonium ions of the quaternary ammonium salts include tetramethylammonium, triethylmethylammonium, and tetraethylammonium. Examples of the quaternized amidiniums include ethyldimethylimidazolinium and tetramethylimidazolinium. Examples of the amines of the amine salts include primary amines, secondary amines, and tertiary amines. Examples of primary amines include methylamine, ethylamine, and propylamine. Examples of secondary amines include dimethylamine, diethylamine, ethylmethylamine, and dibutylamine. Examples of tertiary amines include trimethylamine, triethylamine, tripropylamine, tributylamine, ethyldimethylamine, and ethyldiisopropylamine.

[0108] (Other manufacturing processes) In addition, the anode processing process is a process of producing an anode body, and the cathode processing process is a process of producing a cathode body. The element formation process is a process of producing an element from an anode body, a cathode body, and a separator, and repairing defects that occurred during winding using a chemical conversion treatment. The solid electrolyte attachment process is a process of attaching a conductive polymer to the inside of the element. The seal attachment process is a process of attaching a seal that seals the opening of the outer case that houses the element to the element in advance. The finishing process is a process of sealing the outer case with a seal and repairing defects by applying a voltage.

[0109] (Anode processing process) The anode body is a foil made of a valve metal. In wound electrolytic capacitors, the anode body is a long strip of stretched valve metal, while in laminated electrolytic capacitors or flat-plate electrolytic capacitors, the anode body is a flat plate made of valve metal. 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 included.

[0110] A surface-expanding layer is formed on one or both sides of the anode body. The surface-expanding layer can be an etching layer formed by etching a foil, a sintered layer formed by sintering valve metal powder, or a vapor-deposited layer formed by vapor-depositing valve metal particles onto a foil. The etching layer is formed by tunnel-shaped pits or spongy pits. The tunnel-shaped etching pits are holes dug in the foil thickness direction. These tunnel-shaped etching pits are typically formed by passing a direct current in an acidic aqueous solution containing halogen ions, such as hydrochloric acid. The tunnel-shaped etching pits can be further expanded by passing a direct current in an acidic aqueous solution, such as nitric acid. Furthermore, a surface-expanding layer having spongy etching pits becomes a sponge-like layer with a series of fine voids extending in a space. These spongy etching pits are formed by passing an alternating current in an acidic aqueous solution containing halogen ions, such as hydrochloric acid.

[0111] The sintered layer is produced by obtaining a powder of a valve action metal of the same or different type as the foil by a milling method, atomization method, melt spinning method, rotating disk method, rotating electrode method, etc., forming a paste with a binder or solvent, applying it to the foil, drying it, and heating and sintering it in a vacuum or reducing atmosphere, etc. The atomization method may be any of water atomization method, gas atomization method, and water gas atomization method. 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 of the same or different type as the foil by resistance heat or electron beam energy, and depositing the vapor of the valve action metal particles on the surface of the foil.

[0112] The dielectric coating is formed on one or both sides of the anode body on which the surface-expanding layer is formed. The dielectric coating is typically an oxide coating formed on the surface layer of the anode body. If the anode body is made of aluminum, it is an aluminum oxide layer formed by oxidizing the surface of the surface-expanding layer. In the chemical conversion treatment to form the dielectric coating, a voltage is applied to the anode body in a chemical conversion solution until a desired withstand voltage is achieved. The chemical conversion solution is a solution free of halogen ions, such as a phosphoric acid-based chemical conversion solution such as ammonium dihydrogen phosphate, a boric acid-based chemical conversion solution such as ammonium borate, or an adipic acid-based chemical conversion solution such as ammonium adipate.

[0113] An anode lead extending outside the element is connected to this anode body. The element is an assembly of an anode body, a cathode body, an electrolyte layer, and a separator. After the dielectric film is formed, the anode lead is connected to the anode body by stitching, cold welding, ultrasonic welding, laser welding, or the like. The dielectric film at the intended connection location may be scraped off to expose the bare valve metal, and then the anode lead may be connected.

[0114] (Cathode processing process) In the case of a wound-type electrolytic capacitor, the cathode body is preferably a foil made of a valve metal and stretched. The purity of the cathode body is preferably 99% or higher. A surface-expanding layer is formed on the cathode body, just like on the anode body. Plain foil without a surface-expanding layer may also be used as the cathode body. The cathode body 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 by the cathode body reacting with oxygen in the air. Furthermore, a layer made of metal nitride, metal carbide, or metal carbonitride may be formed on the cathode body by vapor deposition, or a carbon-containing layer may be formed on the surface.

[0115] A cathode lead extending outside the element is connected to the cathode body. The cathode lead is connected to the cathode body by stitching, cold welding, ultrasonic welding, laser welding, etc. If a natural oxide film or a thin oxide film is present, the natural oxide film or the thin oxide film may be scraped off at the intended connection location to expose the bare valve metal, and then the cathode lead may be connected.

[0116] (Element formation process) The anode body and cathode body are stacked with a separator sandwiched between them. The separator is stacked so that one end protrudes beyond one end of the anode body and cathode body. The protruding separator is wound first so that the winding shaft is aligned with the short sides of the anode body and cathode body, creating a winding core. The anode body and cathode body are then wound around this winding core by rolling up the long sides. This winding creates a cylindrical element.

[0117] Examples of separators include cellulose papers such as kraft, Manila hemp, esparto, hemp, and rayon, and mixed papers thereof; polyester-based resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and derivatives thereof; polytetrafluoroethylene-based resins, polyvinylidene fluoride-based resins, vinylon-based resins; polyamide-based resins such as aliphatic polyamides, semi-aromatic polyamides, and wholly aromatic polyamides; polyimide-based resins, polyethylene resins, polypropylene resins, trimethylpentene resins, polyphenylene sulfide resins, acrylic resins, and polyvinyl alcohol resins. These resins can be used alone or in combination.

[0118] The separator separates the anode body and the cathode body to prevent short-circuiting between them. The separator also maintains the electrolyte layer between the anode body and the cathode body. If the shape of the electrolyte layer can be maintained by itself and the cathode body can be separated by the electrolyte layer, the separator can be eliminated from the electrolytic capacitor.

[0119] After the winding, a repair chemical conversion step is provided to repair bare metal portions of the valve metal exposed when the anode body and the cathode body are cut to a desired width, and to repair defects in the dielectric film formed on the anode body caused by physical stress such as winding.

[0120] In the repair and formation process, the element is immersed in a formation solution and a voltage is applied. Examples of the formation solution include a phosphoric acid-based formation solution such as ammonium dihydrogen phosphate, a boric acid-based formation solution such as ammonium borate, an adipic acid-based formation solution such as ammonium adipate, and a formation solution made by mixing boric acid and a dicarboxylic acid such as citric acid. The repair and formation voltage is preferably set to, for example, 0.1 to 1.2 times the formation voltage of the anode body. The voltage application method during repair and formation can be appropriately selected from methods such as applying a constant voltage from the start of repair and formation or increasing the applied voltage stepwise at regular intervals.

[0121] (Solid electrolyte adhesion process) Although there is no restriction on the order in which the solid electrolyte deposition step and the plastic crystal deposition step are performed, it is preferable to first deposit the conductive polymer in the solid electrolyte deposition step and then deposit the plastic crystal. By depositing the conductive polymer first, an electrolyte layer including the plastic crystal and the conductive polymer layer can be formed uniformly, and good capacitance characteristics and good ESR characteristics can be achieved.

[0122] As the conjugated polymer of the conductive 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.

[0123] Among the above conjugated polymers, preferred are conjugated polymers obtained by polymerizing thiophene or its derivatives, 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.

[0124] In particular, a polymer of 3,4-ethylenedioxythiophene, known as EDOT, i.e., poly(3,4-ethylenedioxythiophene), known as PEDOT, is particularly preferred. A substituent may be added to 3,4-ethylenedioxythiophene. For example, alkylated ethylenedioxythiophene, in which an alkyl group having 1 to 5 carbon atoms is added as a substituent, may be used. Examples of alkylated ethylenedioxythiophene include methylated ethylenedioxythiophene (i.e., 2-methyl-2,3-dihydro-thieno[3,4-b][1,4]dioxin), ethylated ethylenedioxythiophene (i.e., 2-ethyl-2,3-dihydro-thieno[3,4-b][1,4]dioxin), butylated ethylenedioxythiophene (i.e., 2-butyl-2,3-dihydro-thieno[3,4-b][1,4]dioxin), and 2-alkyl-3,4-ethylenedioxythiophene.

[0125] 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.

[0126] Examples of polyanions include substituted or unsubstituted polyalkylenes, substituted or unsubstituted polyalkenylenes, substituted or unsubstituted polyimides, substituted or unsubstituted polyamides, and substituted or unsubstituted polyesters, and include polymers consisting only of structural units having anionic groups, and polymers consisting of structural units having anionic groups and structural units not having anionic groups.Specific examples of polyanions include polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallylsulfonic acid, polyacrylic sulfonic acid, polymethacrylic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, polyacrylic acid, polymethacrylic acid, and polymaleic acid.

[0127] In the solid electrolyte deposition process, the conductive polymer is formed in the electrolytic capacitor by using an impregnation method in which the element is impregnated with a conductive polymer liquid in which conductive polymer particles or powder are dispersed or dissolved. The conductive polymer liquid is also applied to the anode body. The conductive polymer liquid may be immersed or applied once or multiple times. The element may be placed in a reduced pressure environment to be impregnated with the conductive polymer liquid. After the conductive polymer liquid is impregnated, the solvent is removed by a drying process. The temperature environment in the drying process is, for example, 40°C or higher and 200°C or lower, and the drying time is, for example, in the range of 3 minutes to 180 minutes. The drying process may be repeated multiple times. Drying may be performed in a reduced pressure environment, for example, by reducing the pressure to 5 kPa to 100 kPa.

[0128] The solvent for the conductive polymer solution may be any solvent that disperses or dissolves the conductive polymer, and is preferably water or a mixture of water and an organic solvent. Examples of the organic solvent include polar solvents, alcohols, esters, hydrocarbons, carbonate compounds, ether compounds, chain ethers, heterocyclic compounds, and nitrile compounds.

[0129] 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.

[0130] The conductive polymer solution may contain a pH adjuster, a polyhydric alcohol, and various additives as needed. The pH adjuster neutralizes the dopant to improve the acidity of the conductive polymer solution so that the anode body, cathode body, and separator do not dissolve. Examples of pH adjusters include ammonia, water-soluble alkylamines such as ethylamine and diethylamine, water-soluble arylamines such as aniline and benzylamine, and water-soluble heterocyclic amines such as pyridine and imidazole. Examples of pH adjusters include alkali metal or alkaline earth metal hydroxides such as sodium hydroxide and calcium hydroxide, alkali metal or alkaline earth metal carbonates such as sodium carbonate and calcium carbonate, and alkali metal or alkaline earth metal alkoxides such as sodium methoxide and calcium methoxide.

[0131] Polyhydric alcohols change the higher-order structure of conductive polymers and enhance the reorientation of the crystalline structure of polymer chains. This reduces the ESR of electrolytic capacitors and improves their withstand voltage. Examples of polyhydric alcohols include sorbitol, ethylene glycol, diethylene glycol, triethylene glycol, polyoxyethylene glycol, glycerin, polyoxyethyleneglycerin, xylitol, erythritol, mannitol, dipentaerythritol, pentaerythritol, and combinations of two or more of these. Because polyhydric alcohols have a high boiling point, they remain in the electrolyte layer even after the conductive polymer liquid is impregnated into the substrate and dried, thereby reducing the ESR and improving the withstand voltage of electrolytic capacitors.

[0132] Examples of the additives include organic binders, surfactants, dispersants, antifoaming agents, coupling agents, antioxidants, and ultraviolet absorbers.

[0133] (Sealing body installation process) The order of the sealing body attachment step after the element formation step is not limited, but for example, the sealing body attachment step can be performed before the plastic crystal attachment step in which the plastic crystal is attached to the element. The sealing body is a roughly disk-shaped body that fits into the opening of the outer case, with through holes that penetrate both sides and are formed at equal intervals around the center line. This sealing body is an elastomer, a hard substrate, a resin layer, or a laminate using two or more of these. In the sealing body attachment step, the anode lead and the cathode lead are inserted into the through holes and pulled out from the sealing body.

[0134] Examples of elastomers include butyl rubber and ethylene propylene diene rubber (EPDM). The elastomer may be primarily butyl rubber, EPDM, or a mixture thereof, and may also contain butyl rubber, isoprene rubber, silicone rubber, ethylene propylene diene rubber (EPDM), fluororubber (FKM), or styrene butadiene rubber (SBR). The elastomer may be crosslinked with a crosslinking agent such as alkylphenol formaldehyde resin, peroxide, quinoid, or sulfur. Furthermore, the elastomer may be mixed with fillers such as mica, talc, calcined clay, silicon hydrate, silicon anhydride, or carbon black.

[0135] The rigid substrate is made of a rigid material such as a metal plate, a synthetic resin plate, or a ceramic plate. The metal plate is made of, for example, aluminum, an aluminum alloy containing aluminum or manganese, or stainless steel, and the synthetic resin plate is made of, for example, a phenolic resin, an epoxy resin, or a polyethylene sulfide resin. Various resins can be used for the resin layer, including epoxy resin, fluororesin, acrylic resin, polyimide resin, silicone resin, phenolic resin, melamine resin, urethane resin, and unsaturated polyester resin.

[0136] (Finishing process) In the finishing process, the sealing body is fitted into the opening of the outer case and then crimped to seal the element in the outer case. After the element is sealed in the outer case, the voltage application process begins, in which a DC voltage is applied to the electrolytic capacitor. This voltage application process repairs defects in the dielectric film. At this time, there are sufficient plastic crystals at the bottom of the etching pit, so defects at the bottom of the etching pit are efficiently repaired.

[0137] In addition to being housed in an exterior case with one end closed and the other end open, the capacitor element may be sealed with a laminate film or molded with resin. Examples of the molding resin include heat-resistant resin and insulating resin. The molding resin may be formed into a thin film using techniques such as dip coating and printing. Furthermore, a flat-plate capacitor element may not require an exterior case.

[0138] (Laminated type) Even in the case of a stacked electrolytic capacitor, a plastic crystal deposition process, which includes a melting process, a molten salt impregnation process, and a crystallization process, is performed. The process order is an anode processing process, a solid electrolyte deposition process, a plastic crystal deposition process, a cathode processing process, and a finishing process. In the anode processing process, an insulating resist layer is printed to prevent the electrolyte layer from forming in the area that will become the anode terminal. Then, the solid electrolyte deposition process and the plastic crystal deposition process are performed.

[0139] In the case of a stacked electrolytic capacitor, the cathode body is preferably a laminate of a metal layer and a carbon layer. In the cathode processing step, a carbon paste is printed on the electrolyte layer using a screen printer or the like and then dried. This drying step forms a carbon layer on the electrolyte layer. Furthermore, a metal paste such as silver paste is printed on the carbon layer and then dried. This drying step forms a silver layer on the carbon layer.

[0140] In the finishing process, the insulating resist layer is peeled off. This can be done by laser irradiation or mechanical peeling using a jig. The exposed area is plated to complete the anode terminal. The element is then covered with a laminate film. Alternatively, the element can be sealed by molding, dip coating, or printing with a resin such as a heat-resistant resin or insulating resin. Finally, a voltage application process is carried out, just like with the wound type. [Example]

[0141] The electrolytic capacitor will be described in more detail below based on examples, but the present invention is not limited to the following examples.

[0142] Example 1 The electrolytic capacitor of Example 1 was fabricated as follows. First, in the anode processing step and the cathode processing step, a pair of electrodes was fabricated using aluminum foil. Both electrode foils were subjected to an etching process to enlarge the surface, forming a surface-enlarged layer. One electrode was used as an anode body, and its surface was enlarged by AC etching. In the anode body surface-enlargement step, an AC current was passed through the aluminum foil in an aqueous solution containing hydrochloric acid to form spongy etching pits. The other electrode was used as a cathode body, and its surface was enlarged by AC etching. In the cathode body surface-enlargement step, an AC current was passed through the aluminum foil in an aqueous solution containing hydrochloric acid to form spongy etching pits.

[0143] For the anode body, a dielectric film was formed on the foil surface by chemical conversion treatment. In the chemical conversion treatment process, aluminum foil with a surface expansion layer was treated in an ammonium adipate solution to form a 63.6V dielectric film on the aluminum foil surface. For the cathode body, a 3V dielectric film was formed on aluminum foil with a surface expansion layer.

[0144] Lead wires were connected to each of the anode and cathode bodies. Next, the device was fabricated by winding the anode and cathode foils facing each other with a manila paper separator between them. The wound assembly had a diameter of 6.3 mm and a height of 5.8 mm. The wound assembly was repaired by passing a voltage of 58 V and a current density of 2 mA through an aqueous ammonium dihydrogen phosphate solution.

[0145] After the element formation process, the process moved to the solid electrolyte deposition process, in which a conductive polymer was deposited between the anode and cathode bodies. In the solid electrolyte deposition process, the wound body was first impregnated with a conductive polymer liquid. The conductive polymer liquid was a dispersion of poly(3,4-ethylenedioxythiophene) (PEDOT / PSS) doped with polystyrene sulfonic acid (PSS). PEDOT / PSS was added at a ratio of 2 wt% to the total conductive polymer liquid. The pH of this conductive polymer liquid was adjusted to 4.0 with ammonia water. In addition, diethylene glycol was added to the conductive polymer liquid at a ratio of 20 wt% to the conductive polymer dispersion liquid.

[0146] The wound body was impregnated with the conductive polymer for 5 minutes at room temperature and in a reduced pressure environment of -0.3 MPa. The impregnation process was performed twice in total. After the wound body was removed from the conductive polymer solution, it was left to stand at room temperature for 10 minutes and then left to stand in a temperature environment of 110°C for 30 minutes to dry the wound body. As a result, an electrolyte layer containing the conductive polymer was formed on the anode body, cathode body, and separator of the wound body.

[0147] After the sealing body attachment process, in which a lead wire connected to a wound body on which an electrolyte layer containing a conductive polymer was formed was passed through a through-hole in the sealing body, the process moved to the plastic crystal attachment process, in which plastic crystals were attached between the anode and cathode bodies in addition to the conductive polymer. P12BScB was used as the plastic crystal. That is, plastic crystals containing P12 cations and BScB anions in a 1:1 molar ratio were attached. The P12 cation is an N-ethyl-N-methylpyrrolidinium cation represented by chemical formula (30). The BScB anion is a bis(salicylate)borate anion represented by chemical formula (22).

[0148] The plastic crystals were added to acetonitrile at a ratio of 50 wt% to the total solution. 90 μl of the acetonitrile solution containing the plastic crystals was poured into the outer case housing the capacitor element. The outer case was then heated, raising the temperature of the acetonitrile solution containing the plastic crystals to 180°C. The melting point of P12BScB plastic crystals is 153°C. Therefore, P12BScB melted inside the outer case and became a molten salt. The acetonitrile then evaporated.

[0149] After the P12BScB was converted into a molten salt, the wound body was placed in an outer case and the P12BScB molten salt was impregnated into the wound body. The impregnation condition was set to 1 minute in an ambient pressure environment. After the P12BScB molten salt was impregnated into the wound body, the P12BScB was cooled to return from the molten salt to a plastic crystal state within the wound body. Since the melting point of P12BScB is 153°C, the cooling condition was set to natural cooling for 5 minutes in a room temperature environment, and plastic crystals were crystallized inside the wound body.

[0150] This resulted in the formation of an electrolyte layer containing a conductive polymer and plastic crystals. The opening of the outer case and the sealing body attached to the wound body were tightly attached by crimping. A voltage application step was then performed on the electrolytic capacitor of Example 1, in which a voltage of 40.25 V was applied for 1 hour in a temperature environment of 105°C. As a result, an electrolytic capacitor with a diameter of 6.3 mm, a height of 5.8 mm, a rated voltage of 35 WV, and 47 μF was produced.

[0151] (Comparative Example 1) An electrolytic capacitor of Comparative Example 1 was produced. The electrolytic capacitor of Comparative Example 1 differed from Example 1 in the plastic crystal deposition process, but all other processes were the same as Example 1. The plastic crystals deposited in Comparative Example 1 were P12BScB, the same as in Example 1. However, in Comparative Example 1, the plastic crystals in the acetonitrile solution were impregnated into the wound body without being melted.

[0152] Specifically, an acetonitrile solution containing crystalline P12BScB was poured into an outer case, and the wound body was then housed in the outer case. The pressure was reduced in the air, allowing the wound body to be impregnated with the acetonitrile solution containing the plastic crystals. The wound body was then exposed to a temperature environment of 45°C for 1 hour, a temperature environment of 60°C for 1 hour, a temperature environment of 85°C for 14 hours, a temperature environment of 100°C for 6 hours, and finally an argon atmosphere at 80°C for 1 hour. This volatilized the solvent in the acetonitrile solution, filling the wound body with plastic crystals without melting them.

[0153] (Example 2 and Comparative Example 2) Electrolytic capacitors of Example 2 and Comparative Example 2 were fabricated. In Example 1 and Comparative Example 1, diethylene glycol was added to the conductive polymer solution, whereas in Example 2 and Comparative Example 2, ethylene glycol was added to the conductive polymer solution at a ratio of 20 wt % relative to the total amount of the conductive polymer solution. Except for the type of additive, the electrolytic capacitor of Example 2 had the same structure and composition as Example 1, and was fabricated using the same manufacturing method and conditions. Furthermore, except for the type of additive, the electrolytic capacitor of Comparative Example 2 had the same structure and composition as Comparative Example 1, and was fabricated using the same manufacturing method and conditions.

[0154] That is, the adhesion method used in the plastic crystal adhesion process of Example 1 and Example 2 is called melt impregnation, and the adhesion method used in the plastic crystal adhesion process of Comparative Example 1 and Comparative Example 2 is called non-melt reduced pressure impregnation. The manufacturing methods of Examples 1 and 2 and Comparative Examples 1 and 2 are as shown in Table 1 below.

[0155] (Table 1) TIFF2025121318000050.tif71166

[0156] In this way, in Examples 1 and 2, the melt impregnation method was used in the plastic crystal attachment step, where the plastic crystals were melted to form a molten salt, which was then impregnated into the wound body and returned to their plastic crystal state within the wound body.In contrast, in Comparative Examples 1 and 2, the non-melt reduced pressure impregnation method was used in the plastic crystal attachment step, where the plastic crystals were impregnated into the wound body in their plastic crystal state.

[0157] (Characteristics test) The electrolytic capacitors of Examples 1 and 2 and Comparative Examples 1 and 2 were measured for capacitance (Cap) and leakage current (LC). The electrolytic capacitors were exposed to a temperature environment of 150°C for 1,500 hours, and the capacitance and leakage current were measured before and after exposure to this high-temperature environment. The state before exposure to the high-temperature environment is referred to as the initial state. The capacitance was measured at 20°C using an LCR meter (model ZM2376, manufactured by NF Corporation). The measurement frequency for Cap was 120 Hz, and the AC current level was a sine wave of 1.0 Vms. The leakage current was measured by measuring the current value after applying a voltage of 35 V for 120 seconds at 20°C.

[0158] The results of the characteristic tests are shown in Table 2 below. (Table 2) TIFF2025121318000051.tif71161

[0159] As shown in Table 2 above, Example 1 exhibits improved capacitance both initially and after exposure to a high-temperature environment, and improved leakage current both initially and after exposure to a high-temperature environment, compared to Comparative Example 1. Furthermore, Example 2 exhibits improved capacitance both initially and after exposure to a high-temperature environment, and improved leakage current both initially and after exposure to a high-temperature environment, compared to Comparative Example 2.

[0160] In particular, Example 1 exhibits better suppression of leakage current after exposure to a high-temperature environment than Comparative Example 1, and Example 2 exhibits better suppression of leakage current after exposure to a high-temperature environment than Comparative Example 2. In Example 2, the leakage current is suppressed to one-tenth or less of that in Comparative Example 2.

[0161] (EDX) The element ratios were measured by energy dispersive X-ray analysis of the cross sections of the anode bodies of Example 1 and Comparative Example 1. The cross sections of the anode bodies were taken along the thickness direction of the foil. The EDX analysis was performed using an energy dispersive X-ray spectrometer (XFlash5060FQ, manufactured by Bruker) with an acceleration voltage of 4 kV, an observation magnification of 10 kx, and a working distance (WD) of 12.0 to 13.0 mm.

[0162] The analysis areas were set at the opening, middle, and bottom of the etching pit. Mapping analysis was then performed for each depth zone. In the mapping analysis, the elemental ratio of boron was measured. Boron is contained in P12BScB, which was adopted as the plastic crystal. Therefore, the elemental ratio of boron at each depth indicates the relative content of plastic crystals at each depth.

[0163] Fig. 3 is a graph showing the results of EDX analysis and illustrating the element ratio of boron in Example 1 and Comparative Example 1. In the graph of Fig. 3, the horizontal axis represents the opening position (top), middle position (middle), and bottom position (bottom) of the etching pit, and the vertical axis represents the element ratio of boron at the middle position and bottom relative to the element ratio of boron at the opening position. In the graph, the circle plots are for Example 1, and the square plots are for Comparative Example 1.

[0164] As shown in FIG. 3, in Comparative Example 1, the amount of boron contained in the bottom of the etching pit is reduced by approximately 26% when the amount of boron contained at the opening position of the etching pit is taken as the standard. In other words, the amount of plastic crystals contained in the bottom of Comparative Example 1 is approximately 74% of that at the opening position. In contrast, in Example 1, the amount of boron contained in the bottom of the etching pit is increased by approximately 7% when the amount of boron contained at the opening position of the etching pit is taken as the standard. In other words, the amount of plastic crystals contained in the bottom of Example 1 is approximately 107% of that at the opening position.

[0165] As a result, in the plastic crystal attachment process, a melting impregnation method is carried out which is divided into a melting process, a molten salt impregnation process, and a crystallization process.In the melting process, the plastic crystal is heated above the melting temperature to turn it into molten salt, in the molten salt impregnation process, the molten salt is impregnated into the element, and in the crystallization process, the molten salt impregnated into the element is cooled and turned back into plastic crystal.It was confirmed that the plastic crystal is contained in an amount of 75% or more at the bottom of the etching pit, based on the content at the opening position of the etching pit.

[0166] (Voltage application process) Electrolytic capacitors were produced in Example 3 and Reference Examples 1 and 2. In Example 1, 20 wt % of diethylene glycol was added to the conductive polymer solution. In contrast, in the manufacturing methods of Example 3 and Reference Examples 1 and 2, 15 wt % of diethylene glycol and 5 wt % of polyethylene glycol were added to the conductive polymer solution relative to the total amount of the conductive polymer solution.

[0167] Example 3 was produced using the same manufacturing method and conditions as Example 1, except for the additives used in the conductive polymer solution. In contrast to Example 3, Reference Examples 1 and 2 differ from Example 3 in the presence or absence of a voltage application step and the order of the voltage application steps. The electrolytic capacitor of Reference Example 1 was produced without the voltage application step. The electrolytic capacitor of Reference Example 2 was produced by applying a voltage identical to that of Example 1 before the plastic crystal deposition step by melt impregnation.

[0168] The electrolytic capacitors of Example 3 and Reference Examples 1 and 2 were measured for capacitance (Cap) and leakage current (LC). The electrolytic capacitors were exposed to a temperature environment of 150°C for 1,500 hours, and the capacitance and leakage current were measured before and after exposure to this high-temperature environment. The state before exposure to the high-temperature environment is referred to as the initial state. The capacitance was measured at 20°C using an LCR meter (manufactured by NF Corporation, model number ZM2376). The Cap measurement frequency was 120 Hz, and the AC current level was a sine wave of 1.0 Vms. The leakage current was measured by applying a voltage of 35 V for 120 seconds at 20°C and then measuring the current value.

[0169] The results of the property tests for Example 3 and Reference Examples 1 and 2 are shown in Table 3 below. (Table 3) TIFF2025121318000052.tif61161

[0170] As shown in Table 3 above, the leakage current of the electrolytic capacitor in Example 3 was suppressed more than in Reference Examples 1 and 2. In Example 3, a voltage was applied to the electrolytic capacitor in the presence of plastic crystals obtained by the melt impregnation method. On the other hand, as shown in Reference Example 2, even when a voltage was applied, the leakage current could not be suppressed well in a situation where only the conductive polymer was present and no plastic crystals were present.

[0171] Based on these results, conductive polymers, which are also solid electrolytes, have little effect in suppressing leakage current in electrolytic capacitors. However, it was confirmed that plastic crystals contained at 75% or more at the bottom of the etching pit, based on the content at the opening of the etching pit, acted effectively on defective areas in the dielectric film, suppressing leakage current in electrolytic capacitors.

Claims

1. an element forming step of forming an element including an anode body and a cathode body having a dielectric coating; a solid electrolyte deposition step of depositing a solid electrolyte onto the anode body; a plastic crystal attachment step of further attaching plastic crystals to the anode body; and The plastic crystal adhesion step includes: a melting step of heating the plastic crystals to a melting temperature or higher to form a molten salt; a molten salt impregnation step of impregnating the element to which the solid electrolyte is attached with the molten salt; a crystallization step of returning the molten salt impregnated in the element to the plastic crystal; having A method for manufacturing an electrolytic capacitor, comprising:

2. The melting temperature of the plastic crystal is higher than the capacitor guarantee temperature; 2. The method for manufacturing an electrolytic capacitor according to claim 1,

3. The melting temperature of the plastic crystals is greater than 150°C; 2. The method for manufacturing an electrolytic capacitor according to claim 1,

4. a voltage application step of applying a voltage to the element after the plastic crystal attachment step; 2. The method for manufacturing an electrolytic capacitor according to claim 1,

5. an anode body having a dielectric film and etching pits; a cathode body facing the anode body; an electrolyte layer including a solid electrolyte and a plastic crystal; Equipped with the plastic crystals are contained in the bottom of the etching pit in an amount of 75% or more based on the content at the opening position of the etching pit; An electrolytic capacitor characterized by:

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