Electrolytic capacitors

Abstract

An electrolytic capacitor comprising a capacitor element and a liquid main component, wherein: the capacitor element is provided with a positive electrode body having a dielectric layer, and a solid electrolyte in contact with the dielectric layer; the liquid main component includes a solvent and a solute; the solvent includes a glycol ether as a first component; the glycol ether includes at least one ether selected from the group consisting of monoalkyl ethers and dialkyl ethers; and the glycol ether has a -(CH2O)n- structure, where n is an integer equal to or greater than 1.

Description

Technical Field

[0001] The present invention relates to an electrolytic capacitor.

Background Art

[0002] As a capacitor that is small, has a large capacitance, and has a low ESR (equivalent series resistance), a hybrid electrolytic capacitor including a solid electrolyte and a liquid component is regarded as promising.

[0003] Patent Document 1 proposes including polyethylene glycol and a compound having a chemical structure of (-CH2-CH(R)-O-) (where R represents an alkyl group having 1 to 4 carbon atoms and n represents an integer) in a capacitor element of a solid electrolytic capacitor.

[0006] Patent Document 2 proposes an electrolytic solution for an electrolytic capacitor in which an organic carboxylate is dissolved in a mixed solvent containing γ-butyrolactone and glycol ether or diglycol ether.

[0004]

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] Electrolytic capacitors are used in various temperature environments. On the other hand, the liquid component is easily affected by temperature changes. In particular, it is important to maintain the low-temperature characteristics of electrolytic capacitors. There is a demand for electrolytic capacitors that can maintain capacitance even at low temperatures (for example, -50°C or lower) in many applications.

Means for Solving the Problems

[0007] One aspect of the present invention is an electrolytic capacitor comprising a capacitor element and a liquid component, wherein the capacitor element comprises an anode having a dielectric layer and a solid electrolyte in contact with the dielectric layer, the liquid component comprises a solvent and a solute, the solvent comprises a glycol ether as a first component, the glycol ether comprises at least one selected from the group consisting of monoalkyl ethers and dialkyl ethers, and the glycol ether is -(CH2O) n -The present invention relates to an electrolytic capacitor having a structure where n is an integer greater than or equal to 1. [Effects of the Invention]

[0008] According to this disclosure, it is possible to provide an electrolytic capacitor containing a liquid component that can maintain good capacitance even at low temperatures.

[0009] While novel features of the present invention are described in the appended claims, the present invention, both in terms of its structure and content, will be better understood by the following detailed description in conjunction with the drawings, in conjunction with other objects and features of the present invention. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic cross-sectional view of an electrolytic capacitor according to one embodiment of the present invention. [Figure 2] This is a schematic diagram illustrating the configuration of the capacitor element according to the same embodiment. [Modes for carrying out the invention]

[0011] The following describes electrolytic capacitors according to embodiments of the present invention, but the electrolytic capacitors according to the present invention are not limited to the following embodiments. In the following description, specific numerical values ​​and materials may be given as examples, but other numerical values ​​and materials may be applied as long as the effects of this disclosure are obtained. In this specification, the description "numerical value A to numerical value B" includes numerical value A and numerical value B, and can be read as "greater than or equal to numerical value A and less than or equal to numerical value B".

[0012] In the following explanation, when lower and upper limits are given as examples for specific physical properties or conditions, any combination of either of the given lower limits and any of the given upper limits is permitted, as long as the lower limit does not exceed the upper limit. When multiple materials are given as examples, unless otherwise specified, one type may be selected and used alone, or two or more types may be used in combination.

[0013] In the following explanation, the terms "contains" or "includes" encompass expressions such as "contains (or includes)," "substantially consists of," and "consists of."

[0014] In the following explanation, "electrolytic capacitor" may be read as "solid electrolytic capacitor" or "hybrid electrolytic capacitor." Also, "capacitor" may be read as "capacitor." Furthermore, "liquid component" may sometimes be read as "electrolyte."

[0015] An electrolytic capacitor according to one embodiment of the present invention comprises a capacitor element and a liquid component. The capacitor element includes an anode having a dielectric layer. The form of the anode is not particularly limited. The anode may be formed, for example, from a metal foil or a porous metal sintered body. The surface layer of the metal foil may have a porous portion. For example, the surface layer of the metal foil may be roughened by etching. The capacitor element may also have a cathode portion.

[0016] The cathode portion includes, for example, a solid electrolyte in contact with the dielectric layer. The solid electrolyte may be a conductive polymer, a conductive inorganic material (such as manganese dioxide), or a TCNQ complex salt.

[0017] The liquid component contains a solvent and a solute. The solvent contains a glycol ether as a first component. The glycol ether contains at least one selected from the group consisting of monoalkyl ethers and dialkyl ethers (hereinafter also referred to as "glycol ether (G)"). Further, the glycol ether (G) has a -(CH2O) n - structure, and n is an integer of 1 or more.

[0018] That is, the monoalkyl ether has an alkyl group at one end and an OH group at the other end, and has a main structural group between the alkyl group and the OH group. The dialkyl ether has alkyl groups at both ends and has a main structural group between the two alkyl groups. The main structural group has an oxyethylene group or a polyoxyethylene group.

[0019] The monoalkyl ether has a structure represented by, for example, R-(CH2O) n -OH. The dialkyl ether has a structure represented by, for example, R-(CH2O) n -R. The two Rs in the dialkyl ether molecule may be the same or different. The glycol ether (G) may be a mixture of a plurality of types of molecules having different n or different Rs.

[0020] Unlike a glycol compound having two OH groups, the glycol ether (G) has only one OH group or no OH group at all. Therefore, the glycol ether (G) is less affected by temperature changes than a glycol compound. By using a liquid component containing the glycol ether (G), an electrolytic capacitor capable of maintaining a good capacitance can be obtained even at a low temperature of, for example, -50°C or lower.

[0021] The glycol ether (G) is preferably liquid at room temperature (25°C) and preferably has a melting point of at least 0°C or lower.

[0022] Furthermore, using glycol ether (G) makes it easier to maintain low ESR and dielectric loss tangent (tanδ) at low temperatures, such as below -50°C. This is thought to be related to the ability to maintain good ionic conductivity of the liquid component at low temperatures. In other words, using glycol ether (G) is thought to improve the overall low-temperature characteristics of electrolytic capacitors, such as below -50°C.

[0023] The main structural group of glycol ether (G) may consist solely of oxyethylene or polyoxyethylene groups, but it may also contain oxyalkylene groups other than oxyethylene groups. However, 60% by mass or more, and even more than 80% by mass (or 100%) of the main structural group consists of oxyethylene or polyoxyethylene groups. Oxyethylene groups are considered advantageous for improving low-temperature properties because they contribute to improved ionic conductivity and have lower volatility compared to other oxyalkylene groups. It is believed that a higher ratio of oxygen to carbon in the main structural group improves ionic conductivity and is advantageous for increasing capacity.

[0024] Glycol ethers (G) have a lower probability of forming hydrogen bonds and are less likely to undergo esterification reactions than glycol compounds. Therefore, glycol ethers (G) are considered to be less affected by temperature changes than glycol compounds. In particular, the formation of hydrogen bonds is thought to increase the viscosity of the liquid component at low temperatures and decrease its ionic conductivity.

[0025] Dialkyl ethers that do not contain any OH groups are considered to be less affected by temperature changes than monoalkyl ethers that contain one OH group. On the other hand, monoalkyl ethers that contain one OH group are less permeable to sealing materials than dialkyl ethers, and are therefore considered to have the effect of significantly suppressing the evaporation of liquid components of electrolytic capacitors. From the viewpoint of obtaining better low-temperature characteristics, it is desirable that the content of dialkyl ether in glycol ether (G) exceeds 50% by mass, and it is also acceptable for it to be 90% by mass or more. From the viewpoint of obtaining good low-temperature characteristics and suppressing the evaporation of liquid components, the content of monoalkyl ether in glycol ether (G) may be 10% by mass or more, and even 20% by mass or more.

[0026] Structure - (CH2O) n In this case, n should be 1 or greater, but the average value of n may be, for example, 3 or greater, 4 or greater, or 5 or greater. The average value of n may also be, for example, 20 or less, 15 or less, or 10 or less. If the n value is within this range, the viscosity of the liquid component containing glycol ether (G) can be kept lower. Furthermore, better ionic conductivity of the liquid component can be maintained. In particular, it is desirable that 90% or more by mass of the glycol ether has an integer n within the range of 1 to 11.

[0027] The alkyl group (e.g., R-(CH2O)) of the glycol ether (G) n -OH and R-(CH2O) n From the viewpoint of ensuring sufficient ionic conductivity, the R group of -R is preferably a C1-C10 alkyl group having 1 to 10 carbon atoms. Here, "Cn1-Cn2 alkyl group" is a general term for alkyl groups having n1 (where n1 is an integer) to n2 (where n2 is an integer greater than n1). For example, "C1-C3 alkyl group" means at least one selected from the group consisting of a methyl group, an ethyl group, an n-propyl group, and an iso-propyl group. The alkyl group (R) may also be a C1-C5 alkyl group or a C1-C3 alkyl group.

[0028] 90 mol% or more of the alkyl groups in the glycol ether (G) may be C1-C10 alkyl groups. For example, if the amount of glycol ether (G) in the liquid component of a certain electrolytic capacitor is x1 mole, and y mole% of the glycol ether (G) is a dialkyl ether and (100-y) mole% is a monoalkyl ether, then the liquid component will contain (2 × x1 × y / 100) + (x1 × (100-y) / 100 ) moles of alkyl group are included. In that case, 0.9 × {(2 × x 1 × y / 100) + (x 1 × (100-y) / 100) More than} moles may be C1-C10 alkyl groups, C1-C5 alkyl groups, or C1-C3 alkyl groups.

[0029] Similarly, 90 mol% or more of the alkyl groups of the monoalkyl ether in glycol ether (G) may be C1-C10 alkyl groups, C1-C5 alkyl groups, or C1-C3 alkyl groups.

[0030] Similarly, 90 mol% or more of the alkyl groups of the dialkyl ether may be independently C1-C10 alkyl groups, C1-C5 alkyl groups, or C1-C3 alkyl groups.

[0031] The number-average molecular weight Mn of glycol ether (G) may be, for example, 100 or more, 150 or more, or 200 or more. The number-average molecular weight Mn may also be, for example, 4000 or less, 2000 or less, or 1000 or less. Within this range of number-average molecular weight Mn, the viscosity of the liquid component containing glycol ether (G) can be maintained at a lower level. Furthermore, better ionic conductivity of the liquid component can be maintained. Among these, a number-average molecular weight of 100 or more and 1000 or less is desirable for the glycol ether.

[0032] As a solvent, only glycol ether (G) may be used, or other components may be used. However, from the viewpoint of obtaining better capacitance at low temperatures of -50°C or below, the content of glycol ether (G) in the liquid component may be 10% by mass or more, 15% by mass or more, or 20% by mass or more. The content of glycol ether (G) in the liquid component may be 95% by mass or less, 90% by mass or less, or 70% by mass or less.

[0033] The solvent preferably contains at least one component selected from the group consisting of ethylene glycol and sulfolane (hereinafter also referred to as the "second component"), in addition to glycol ether (G).

[0034] Ethylene glycol is thought to have the effect of suppressing the evaporation of liquid components in electrolytic capacitors because it does not easily permeate sealing materials even at high temperatures. Furthermore, when a conductive polymer is used as a solid electrolyte, ethylene glycol is thought to have the effect of improving the crystallinity of the conductive polymer and thereby enhancing its conductivity. In addition, ethylene glycol has excellent thermal conductivity and excellent heat dissipation when ripple current is generated.

[0035] Sulfolanes are stable at high temperatures and can contribute to reducing the viscosity of liquid components. Although sulfolanes can solidify at low temperatures, using them in combination with glycol ethers (G) can suppress this phenomenon while still allowing the benefits of sulfolanes to be enjoyed.

[0036] The content of the second component in the liquid component may be, for example, 5% by mass or more, or 20% by mass or more. The content of the second component in the liquid component may be, for example, 90% by mass or less, or 60% by mass or less.

[0037] The solvent may also contain γ-butyrolactone (hereinafter also referred to as "third component") as a component other than glycol ether (G). γ-butyrolactone is stable over a wide temperature range and has low viscosity. The content of the third component in the liquid component may be, for example, 5% by mass or more, or 20% by mass or more. The content of the third component in the liquid component may also be, for example, 70% by mass or less, or 50% by mass or less.

[0038] The solvent may contain a fourth component in addition to the components described above. However, it is desirable to limit the content of the fourth component in the liquid component to 20% by mass or less. Examples of the fourth component include glycol compounds other than ethylene glycol, sulfone compounds other than sulfolane, lactone compounds other than γ-butyrolactone, and carbonate compounds. Examples of glycol compounds include propylene glycol, trimethylene glycol, 1,4-butanediol, pentanediol, and hexanediol. Examples of sulfone compounds include linear sulfones (dimethyl sulfone, diethyl sulfone, etc.) and cyclic sulfones (3-methylsulfolane, 3,4-dimethylsulfolane, 3,4-diphenylmethylsulfolane, etc.). An example of a lactone compound is γ-valerolactone. Examples of carbonate compounds include dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, and fluoroethylene carbonate. The fourth component may be used alone or in combination of two or more types.

[0039] When using the first and second components together, it is desirable to consider their proportions so that each component exhibits the characteristics described above. For example, the mass of the first component may be 0.1 times or more and 5 times or less than the mass of the second component, or 0.2 times or more and 2 times or less. By controlling the mass ratio of the first and second components, it becomes possible to improve the low-temperature characteristics more significantly and in a balanced manner.

[0040] Examples of preferred solvent compositions for the liquid component include the following: (i) A solvent in which 90% or more by mass of glycol ether (G) is a dialkyl ether.

[0041] (ii) A solvent in which 90% by mass or more of the dialkyl ether in glycol ether (G) is polyethylene glycol dialkyl ether.

[0042] (iii) 90% by mass or more of the dialkyl ether in glycol ether (G) is polyethylene A ethylene glycol dialkyl ether solvent in which 90 mol% or more of the alkyl groups in polyethylene glycol dialkyl ether are C1-C10 alkyl groups, C1-C5 alkyl groups, or C1-C3 alkyl groups.

[0043] (iv) 90% by mass or more of glycol ether (G) is ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, pentaethylene glycol monomethyl ether, hexaethylene glycol monomethyl ether, heptaethylene glycol monomethyl ether, octaethylene glycol monomethyl ether, nonaethylene glycol monomethyl ether, dodecaethylene glycol monomethyl ether, polyethylene glycol monomethyl ether 400, polyethylene glycol monomethyl ether 550, polyethylene glycol monomethyl ether 1000, polyethylene glycol monomethyl ether 2000, polyethylene glycol monomethyl ether 4000, ethylene glycol di A solvent that is at least one selected from the group consisting of methyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether 240, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, ethylene glycol diethyl ether, diethylene glycol diethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, ethylene glycol dibutyl ether, diethylene glycol dibutyl ether, ethylene glycol monohexyl ether, and diethylene glycol monohexyl ether.

[0044] (v) 90% by mass or more of glycol ether (G) is polyethylene glycol monomethyl A solvent selected from the group consisting of polyethylene glycol monomethyl ether 400, polyethylene glycol monomethyl ether 550, polyethylene glycol monomethyl ether 1000, polyethylene glycol monomethyl ether 2000, polyethylene glycol monomethyl ether 4000, polyethylene glycol dimethyl ether 200, polyethylene glycol dimethyl ether 240, polyethylene glycol dimethyl ether 400, polyethylene glycol dimethyl ether 550, polyethylene glycol dimethyl ether 1000, polyethylene glycol dimethyl ether 2000, and polyethylene glycol dimethyl ether 4000.

[0045] Here, the value of "Mn" in the notation "polyethylene glycol monomethyl ether Mn" or "polyethylene glycol dimethyl ether Mn" indicates the number-average molecular weight. Mn represents a numerical range of Mn × 0.8 or greater and Mn × 1.2 or less. For example, "polyethylene glycol dimethyl ether 400" means polyethylene glycol dimethyl ether with a number-average molecular weight of 320 to 480.

[0046] Note that Mn is the number-average molecular weight in polystyrene terms, calculated using gel permeation chromatography.

[0047] The solute contains an acidic component and a basic component. A salt of the acidic component and the basic component (electrolyte salt) may be used as the solute. At least a portion of the electrolyte salt dissociates in the liquid component to generate cations and anions. The inclusion of acidic and basic components in the solute increases the degree of ion dissociation, thereby improving the repairability of the dielectric layer. When preparing the liquid component, the electrolyte salt may be added to the solvent, or the acidic component and the basic component may be added, or the electrolyte salt may be added along with the acidic component and / or the basic component.

[0048] Organic acids are preferred as the acid component. Examples of organic acids include organic carboxylic acids or their anhydrides. Examples of organic acids include aromatic carboxylic acids, aliphatic carboxylic acids, and alicyclic carboxylic acids. Examples of aromatic carboxylic acids include phthalic acid, isophthalic acid, terephthalic acid, benzoic acid, salicylic acid, trimellitic acid, and pyromellitic acid. fat Examples of alicyclic carboxylic acids include maleic acid and adipic acid. Examples of alicyclic carboxylic acids include hydrides of aromatic carboxylic acids. Phthalic acid is preferred from the viewpoint of high repairability and thermal stability of the dielectric layer. The acid component may be used alone or in combination of two or more types.

[0049] Organic bases are preferred as the base component. Examples of organic bases include amine compounds, quaternary amidinium compounds, and quaternary ammonium compounds. The amine compound may be a primary, secondary, or tertiary amine. Examples of amine compounds include aliphatic amines, aromatic amines, and heterocyclic amines. The base component may be used alone or in combination of two or more types.

[0050] Specific examples of amine compounds include methylamine, dimethylamine, monoethyldimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethylenediamine, N,N-diisopropylethylamine, tetramethylethylenediamine, hexamethylenediamine, spermidine, spermine, amantadine, aniline, phenethylamine, toluidine, pyrrolidine, piperidine, piperazine, morpholine, imidazole, imidazoline, pyridine, pyridazine, pyrimidine, pyrazine, and 4-dimethylaminopyridine.

[0051] As quaternary amidinium compounds, quaternary derivatives of cyclic amidine compounds are preferred, such as imidazolium compounds and imidazolinium compounds. Examples of quaternary imidazolium compounds include 1,3-dimethylimidazolium, 1,2,3-trimethylimidazolium, 1-ethyl-3-methylimidazolium, 1-ethyl-2,3-dimethylimidazolium, 1,3-diethylimidazolium, 1,2-diethyl-3-methylimidazolium, and 1,3-diethyl-2-methylimidazolium. Examples of quaternary imidazolinium compounds include 1,3-dimethylimidazolinium, 1,2,3-trimethylimidazolinium, 1-ethyl-3-methylimidazolinium, 1-ethyl-2,3-dimethylimidazolinium, 1,3-diethylimidazolinium, 1,2-diethyl-3-methylimidazolinium, 1,3-diethyl-2-methylimidazolinium, and 1,2,3,4-tetramethylimidazolinium.

[0052] Preferred quaternary ammonium compounds include, for example, diethyldimethylammonium and monoethyltrimethylammonium.

[0053] From the viewpoint of suppressing degradation of the solid electrolyte and improving the repairability of the dielectric layer, the molar ratio of the acid component to the basic component (= acid component / basic component) is preferably 1.1 or more and 10.0 or less.

[0054] The concentration of the acid component in the liquid component is preferably 0.1% by mass or more and 30% by mass or less, and more preferably 1% by mass or more and 20% by mass or less. The concentration of the base component in the liquid component is preferably 0.1% by mass or more and 20% by mass or less, and more preferably 1% by mass or more and 15% by mass or less. In these cases, the repairability of the dielectric layer can be further improved.

[0055] The present invention will be described more specifically below based on embodiments. However, the following embodiments are not intended to limit the present invention.

[0056] Figure 1 is a schematic cross-sectional view of an electrolytic capacitor according to this embodiment, and Figure 2 is a schematic diagram showing a part of the capacitor element related to the electrolytic capacitor unfolded. In the following description, a cylindrical electrolytic capacitor will be used as an example, but the form of the electrolytic capacitor is not particularly limited.

[0057] An electrolytic capacitor comprises, for example, a capacitor element 10, a cylindrical case 11 housing the capacitor element 10, a sealing member 12 closing the opening of the case 11, a base plate 13 covering the sealing member 12, lead wires 14A and 14B leading out from a through hole 12a in the sealing member 12 and passing through the base plate 13, and lead tabs 15A and 15B connecting the lead wires 14A and 14B to the electrodes of the capacitor element 10. The area near the opening end of the case 11 is tapered inward, and the opening end is curled so as to be crimped to the sealing member 12.

[0058] The capacitor element 10 is manufactured from a wound body as shown in Figure 2. The wound body comprises an anode 21 connected to a lead tab 15A, a cathode 22 connected to a lead tab 15B, and a separator 23. The wound body is a semi-finished product in which a solid electrolyte is not formed between the anode 21 and the cathode 22.

[0059] The anode 21 and cathode 22 are wound around a separator 23. The outermost circumference of the winding is secured with a winding stopper tape 24. Figure 2 shows the winding in a partially unfolded state before securing the outermost circumference.

[0060] The anode 21 comprises a roughened metal foil such that its surface is uneven or its surface layer is porous. A dielectric layer is formed on the metal foil having the uneven or porous surface. A solid electrolyte is attached to at least a portion of the surface of the dielectric layer. The solid electrolyte may also cover at least a portion of the surface of the cathode 22 and / or the surface of the separator 23. The capacitor element 10 with the solid electrolyte is housed in a case 11 together with a liquid component (not shown).

[0061] (Liquid component) The liquid component contains a solvent and a solute. The liquid component can be prepared by mixing its constituent components. The liquid component can be any of the liquid components described above.

[0062] (Capacitor element) The capacitor element 10 comprises an anode having a dielectric layer, a cathode, and a solid electrolyte in contact with the dielectric layer. The capacitor element 10 typically includes a separator interposed between the anode and the cathode.

[0063] (Anode) As previously described, the anode may be, for example, a metal foil with a roughened surface. The type of metal constituting the metal foil is not particularly limited, but it is preferable to use valve metals such as aluminum, tantalum, or niobium, or alloys containing valve metals, from the standpoint of facilitating the formation of a dielectric layer.

[0064] Surface roughening of the metal foil can be carried out by known methods. Roughening creates multiple irregularities on the surface of the metal foil. Surface roughening is preferably carried out by etching the metal foil, for example. Etching may be carried out by methods such as DC electrolysis or AC electrolysis.

[0065] (Dielectric layer) The dielectric layer is formed on the surface of the anode. Specifically, since the dielectric layer is formed on the surface of the roughened metal foil, it forms along the inner walls of holes and depressions (pits) on the surface of the anode.

[0066] The method for forming the dielectric layer is not particularly limited, but it can be formed by chemical conversion treatment of a metal foil. The chemical conversion treatment may be carried out, for example, by immersing the metal foil in a chemical conversion solution such as an ammonium adipate solution. During the chemical conversion treatment, a voltage may be applied while the metal foil is immersed in the chemical conversion solution, if necessary.

[0067] Typically, for mass production purposes, metal foils formed from large sheets of valve metal or similar material are subjected to surface roughening and chemical conversion treatments. In this case, the treated foil is cut to the desired size to prepare an anode body with a dielectric layer.

[0068] (Cathole body) For the cathode, for example, a metal foil is used. The type of metal is not particularly limited, but it is preferable to use a valve metal or an alloy containing a valve metal such as aluminum, tantalum, or niobium. The cathode may be subjected to roughening and / or chemical conversion treatment as needed. Roughening and chemical conversion treatment can be carried out, for example, by the method described for the anode.

[0069] (Separator) The separator is not particularly limited, and may be a nonwoven fabric containing fibers of cellulose, polyethylene terephthalate, vinylon, or polyamide (e.g., aliphatic polyamide, aromatic polyamide such as aramid).

[0070] (solid electrolyte) The solid electrolyte includes, for example, a conductive polymer. As the conductive polymer, for example, a π-conjugated polymer may be used. The conductive polymer may also include a π-conjugated polymer and a dopant.

[0071] Examples of π-conjugated polymers that can be used include polypyrrole, polythiophene, polyfuran, polyaniline, and their derivatives. A derivative refers to a polymer that uses polypyrrole, polythiophene, polyfuran, polyaniline, etc., as its basic skeleton. For example, polythiophene derivatives include poly(3,4-ethylenedioxythiophene) (PEDOT).

[0072] As the dopant, polymers such as polystyrene sulfonic acid (PSS) may be used, as well as naphthalene sulfonic acid, toluene sulfonic acid, etc.

[0073] The conductive polymer may be formed, for example, by chemical polymerization and / or electrochemical polymerization of a conjugated polymer precursor (monomer, oligomer, etc.) on a dielectric layer. In this case, the conjugated polymer precursor and the dopant may be present together. A solution containing the conductive polymer (and dopant), or a dispersion containing the conductive polymer (and dopant), may be applied to the dielectric layer and dried to form a solid electrolyte.

[0074] (others) The capacitor element 10 can be manufactured by known methods. For example, the capacitor element 10 may be manufactured by stacking an anode and a cathode, each having a dielectric layer, via a separator, and then forming a solid electrolyte layer between the anode and the cathode. Alternatively, it may be manufactured by winding an anode and a cathode, each having a dielectric layer, via a separator to form a wound body as shown in Figure 2, and then forming a solid electrolyte layer between the anode and the cathode. When forming the wound body, lead tabs 15A and 15B may be wound in, thereby causing the lead wires 14A and 14B to protrude from the wound body as shown in Figure 2.

[0075] Of the anode, cathode, and separator, the outermost layer of the winding (cathode 22 in Figure 2) has its outer surface end secured with winding tape. If the anode is prepared by cutting a large sheet of metal foil, a further chemical treatment may be performed on the capacitor element in its winding state to provide a dielectric layer on the cut surface of the anode.

[0076] An electrolytic capacitor can be manufactured by housing a capacitor element 10 and a prepared liquid component in a case 11, and sealing the opening of the case 11 with a sealing member 12.

[0077] [Examples] The present invention will be described in detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0078] Examples 1-8 In this example, a wound electrolytic capacitor (10 mm in diameter x 10 mm in length) with a rated voltage of 63 V and a rated capacitance of 82 μF was fabricated. The specific manufacturing method of the electrolytic capacitor is described below.

[0079] (Fabrication of capacitor elements) A dielectric layer was formed on an aluminum foil (anode) with a roughened surface by chemical conversion treatment using an ammonium adipate solution. The resulting anode foil was cut to a predetermined size. Lead tabs were attached to the aluminum foil used as the anode foil and cathode foil, respectively. The anode foil and cathode foil were wound together with a separator in between, and the outer surface was secured with winding tape to create a wound body. At this time, the lead tabs and lead wires integrated with the lead tabs were pulled out from the wound body, and the lead tabs were wound while being incorporated into the winding. The wound body was further chemically converted using an ammonium adipate solution.

[0080] A winding was immersed for 5 minutes in a dispersion containing polyethylenedioxythiophene (conductive polymer), polystyrene sulfonic acid (dopant), and water, which was contained in a designated container. After that, the winding was removed from the dispersion. Next, the dispersion-impregnated winding was dried in a 150°C drying oven for 20 minutes, allowing the conductive polymer and dopant to adhere between the anode and cathode foils of the winding. In this way, the capacitor element was completed and housed in a bottomed cylindrical case with a diameter of 10 mm and a length of 10 mm.

[0081] (Impregnation with liquid components) The liquid component was poured into the case and impregnated into the capacitor element under reduced pressure (40 kPa). The liquid component used was a solution prepared by dissolving triethylamine phthalate salt as the solute (electrolyte salt) in a solvent with the composition shown in Table 1. The concentration of the electrolyte salt in the liquid component was uniformly set to 13% by mass (total of solute (electrolyte salt) + solvent = 100%).

[0082] (Sealing of capacitor elements) An electrolytic capacitor was completed by sealing a capacitor element impregnated with a liquid component. Specifically, the capacitor element was housed in a bottomed case so that the lead wires were positioned on the opening side of the bottomed case, and a sealing member (an elastic material containing butyl rubber as the rubber component) formed to allow the lead wires to pass through was placed above the capacitor element to seal the capacitor element inside the bottomed case. Then, a drawing process was performed near the opening end of the bottomed case, and the opening end was further curled, and a base plate was placed on the curled portion to complete the electrolytic capacitor shown in Figure 1. After that, an aging process was performed while applying voltage.

[0083] Comparative Example 1 Except for using polyethylene glycol (Mn:200) instead of glycol ether, the liquid components were prepared in the same manner as in Example 1, and an electrolytic capacitor was assembled.

[0084] Comparative Example 2 Except for using polyethylene glycol (Mn:400) instead of glycol ether, the liquid components were prepared in the same manner as in Example 1, and an electrolytic capacitor was assembled.

[0085] [evaluation] Using the electrolytic capacitors obtained in the examples and comparative examples, the capacitance, tanδ, and ESR were measured at 20°C and -55°C at 120Hz using the following procedure, and the rate of change was calculated with the value at 20°C set to 100%. The results are shown in Table 2. Examples 1 to 8 are A1 to A8, respectively, and comparative examples 1 to 2 are B1 to B2, respectively. The tests were performed on 10 electrolytic capacitors randomly selected from the 100 capacitors fabricated in each example, and the average value was calculated.

[0086] [Table 1]

[0087] The meanings of the abbreviations in Tables 1 and 2 are as follows: EG: Ethylene glycol SL: Sulfolane PEG: Polyethylene glycol MME: Monomethyl ether DME: Dimethyl ether The numbers following PEG, MME, and DME (200, 300, 400) represent the number-average molecular weight. Capacitance: Capacitance

[0088] [Table 2]

[0089] As shown in Tables 1 and 2, even at room temperature (20°C), Examples A1 to A8 tend to have slightly larger capacitances and slightly smaller tanδ and ESRs than Comparative Examples B1 to B2. However, the superiority of the Examples at room temperature is only slight. On the other hand, at minus 55°C, Examples A1 to A8 tend to have significantly larger capacitances and significantly smaller tanδ and ESRs than Comparative Examples B1 to B2. In particular, the capacitance at low temperatures increases significantly when dialkyl ether is used. Furthermore, by using the second component in combination with the first component, a further improvement in capacitance can be observed. In particular, when dialkyl ether is used as the first component and the second component is used in combination, a good balance of low-temperature characteristics was obtained. [Industrial applicability]

[0090] The electrolytic capacitor according to the present invention has high capacitance even at low temperatures (for example, temperatures below -50°C) and excellent low-temperature characteristics, making it suitable for a variety of applications.

[0091] Although the present invention has been described in relation to preferred embodiments at present, such disclosure should not be interpreted restrictively. Various modifications and alterations will undoubtedly become apparent to those skilled in the art in the field to which the invention pertains by reading the above disclosure. Accordingly, the appended claims should be interpreted as encompassing all modifications and alterations without departing from the true spirit and scope of the invention. [Explanation of Symbols]

[0092] 10: Capacitor element, 11: Case, 12: Sealing material, 13: Base plate, 14A, 14B: Lead wires, 15A, 15B: Lead tabs, 21: Anode, 22: Cathode, 23: Separator, 24: Retaining tape

Claims

1. An electrolytic capacitor comprising a capacitor element and a liquid component, The capacitor element comprises an anode having a dielectric layer and a solid electrolyte in contact with the dielectric layer. The aforementioned liquid component comprises a solvent and a solute. The solvent comprises glycol ether as a first component. The glycol ether comprises at least one selected from the group consisting of monoalkyl ethers and dialkyl ethers. The content of the glycol ether in the liquid component is 20% by mass or more. An electrolytic capacitor wherein the solvent further comprises, as a second component, at least one selected from the group consisting of glycol compounds and sulfone compounds.

2. The electrolytic capacitor according to claim 1, wherein the content of the glycol ether in the liquid component is 20% by mass or more (except when it is 40% by mass or less).

3. The electrolytic capacitor according to claim 1, wherein the second component comprises at least a sulfone compound.

4. The electrolytic capacitor according to claim 1, wherein the content of the second component in the liquid component is 60% by mass or less.

5. The electrolytic capacitor according to claim 1, wherein 90% by mass or more of the glycol ether has an integer n in the range of 1 to 11.

6. The electrolytic capacitor according to claim 1, wherein the number-average molecular weight of the glycol ether is 100 or more and 1000 or less.

7. The electrolytic capacitor according to claim 1, wherein the content of the dialkyl ether in the glycol ether exceeds 50% by mass.

8. The electrolytic capacitor according to any one of claims 1 to 7, wherein 90 mol% or more of the alkyl groups in the glycol ether are C1-C10 alkyl groups having 1 to 10 carbon atoms.

9. The electrolytic capacitor according to claim 8, wherein 90 mol% or more of the alkyl group of the monoalkyl ether is a C1-C10 alkyl group.

10. The electrolytic capacitor according to claim 8, wherein 90 mol% or more of the alkyl groups of the dialkyl ether are independently C1-C10 alkyl groups.

11. The electrolytic capacitor according to any one of claims 1 to 7, wherein the content of the glycol ether in the liquid component is 70% by mass or less.

12. The electrolytic capacitor according to any one of claims 1 to 7, wherein the solvent further comprises γ-butyrolactone as a third component.

13. The electrolytic capacitor according to any one of claims 1 to 7, wherein the mass of the first component is five times or less the mass of the second component.

14. The electrolytic capacitor according to any one of claims 1 to 7, wherein the solute comprises an acidic component and a basic component.

15. 90% by mass or more of the dialkyl ether is polyethylene glycol dialkyl ether. The electrolytic capacitor according to any one of claims 1 to 7, wherein 90 mol% or more of the alkyl groups in the polyethylene glycol dialkyl ether are C1-C10 alkyl groups having 1 to 10 carbon atoms.

16. 90% by mass or more of the glycol ether is ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, pentaethylene glycol monomethyl ether, hexaethylene glycol monomethyl ether, heptaethylene glycol monomethyl ether, octaethylene glycol monomethyl ether, nonaethylene glycol monomethyl ether, dodecaethylene glycol monomethyl ether, polyethylene glycol monomethyl ether 400, polyethylene glycol monomethyl ether 550, polyethylene glycol monomethyl ether 1000, polyethylene glycol monomethyl ether 2000, polyethylene glycol monomethyl ether 4000, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether An electrolytic capacitor according to any one of claims 1 to 7, wherein the electrolytic capacitor is at least one selected from the group consisting of ethylene glycol dimethyl ether 200, polyethylene glycol dimethyl ether 240, polyethylene glycol dimethyl ether 400, polyethylene glycol dimethyl ether 550, polyethylene glycol dimethyl ether 1000, polyethylene glycol dimethyl ether 2000, polyethylene glycol dimethyl ether 4000, ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monoethyl ether, ethylene glycol diethyl ether, diethylene glycol diethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, ethylene glycol dibutyl ether, diethylene glycol dibutyl ether, ethylene glycol monohexyl ether, and diethylene glycol monohexyl ether.

Images