Method for forming an ultra-high voltage solid electrolytic capacitor

Abstract

A method of forming an ultra-high voltage solid electrolytic capacitor element (33), the method comprising: anodically oxidizing a sintered porous anode body at a forming voltage of 300 volts to 380 volts and a temperature of 25°C to 50°C to form an anode including a dielectric coating on the anode body, the anode body being formed from a powder containing tantalum, niobium, or an electrically conductive oxide thereof; and Applying a dispersion of conductive polymer particles to the anode to form a solid electrolyte, wherein the conductive polymer particles contain a substituted polythiophene.

Description

Background of the invention

[0001] Solid electrolytic capacitors (e.g., tantalum capacitors) have made a significant contribution to the miniaturization of electronic circuits and enabled the application of such circuits in extreme environments. Conventional solid electrolytic capacitors can be formed by pressing a metal powder (e.g., tantalum) around a metal lead wire, sintering the pressed part, anodizing the sintered anode, and then applying a solid electrolyte. Intrinsically conductive polymers are often used as solid electrolytes due to their advantageously low equivalent series resistance ("ESR") and "non-burning / non-ignition" failure mode. Such electrolytes can be formed by in-situ polymerization of the monomer in the presence of a catalyst and a dopant. Alternatively, preformed slurries of conductive polymer can be used.Regardless of how they are formed, one problem with conductive polymer electrolytes is that they are inherently weak, which can sometimes lead to them delaminating from the dielectric during capacitor formation or during operation. Furthermore, in very high-voltage applications, the quality of the dielectric layer can cause part failure. For example, high-voltage power distribution systems deliver a high voltage to the capacitor, which can result in an inrush or surge current, particularly during rapid turn-on or an operating current spike. The peak surge current a capacitor can withstand without failure may be related in part to the quality of the dielectric. Because the thinner regions have lower resistance than the thicker adjacent regions, the power dissipation in the thinner regions is generally greater.Therefore, when subjected to a surge current, the thinner areas can develop into weak “hot spots” that eventually lead to deterioration and breakdown of the dielectric.

[0002] DE 10 2007 048 212 A1, which represents the closest prior art, relates to a method for producing an electrolytic capacitor with low equivalent series resistance and low leakage current. The electrolytic capacitor consists of a solid electrolyte, an intermediate layer, and an outer layer containing conductive polymers. According to the disclosed method, a sintered porous anode body is anodically oxidized to form an anode, with a dielectric coating being present on the anode body. The anode body is formed from a powder containing tantalum, niobium, or an electrically conductive oxide thereof. Subsequently, a dispersion containing particles of a conductive polymer is applied to the anode to form a solid electrolyte, said particles containing a substituted polythiophene.

[0003] DE 10 2011 105 702 A1 discloses a solid electrolytic capacitor comprising an anode body formed from an electrically conductive powder, a dielectric coating covering the anode body, and a solid electrolyte coating the dielectric and comprising a manganese oxide layer. According to the disclosure, the uniformity and consistency of the coating of the dielectric with the solid electrolyte is significantly improved by using a dispersant in the precursor solution for the manganese oxide layer, which contributes to minimizing the likelihood of the manganese oxide precursor forming droplets upon contact with the surface of the dielectric.

[0004] Therefore, there is currently a need for a solid electrolytic capacitor that has improved performance in very high voltage environments. Summary of the invention

[0005] According to one embodiment of the present invention, a method for forming an ultrahigh-voltage solid electrolytic capacitor element is disclosed. The method comprises anodically oxidizing a sintered porous anode body at a forming voltage of about 300 volts to about 380 volts and a temperature of about 25°C to about 50°C to form an anode including a dielectric coating on the anode body, wherein the anode body is formed from a powder containing tantalum, niobium, or an electrically conductive oxide thereof; and applying a dispersion of conductive polymer particles to the anode to form a solid electrolyte, wherein the conductive polymer particles include a substituted polythiophene.

[0006] Other features and aspects of the present invention are set forth in more detail below. Short description of the drawing

[0007] A full and illustrative statement of the present invention, including the best form thereof, directed to one of ordinary skill in the art is given with particular reference to the remainder of the specification, which refers to the accompanying figures, in which: Fig. 1 is a schematic representation of an embodiment of a capacitor that may be formed in accordance with the present invention; and Fig. Figure 2 is a diagram of a shock absorbing circuit.

[0008] The repeated use of reference symbols in the present description and the drawings is intended to represent the same or analogous features or elements of the invention. Detailed description of representative embodiments

[0009] It will be understood by one of ordinary skill in the art that the present discussion is merely a description of exemplary embodiments and is not intended to limit the broader aspects of the present invention. These broader aspects are included in the exemplary structure.

[0010] Generally speaking, the present invention relates to a capacitor for use in ultra-high voltage environments, such as voltage ratings of about 75 volts or more, in some embodiments about 100 volts or more, and in some embodiments from about 110 volts to about 200 volts. The present inventors have discovered that the ability to achieve such ultra-high voltages can be achieved through a unique and controlled combination of features related to the formation of the anode, the dielectric, and the solid electrolyte. For example, the present inventors have discovered that anodic oxidation can be carried out at a higher formation voltage and lower temperatures than those conventionally used.Namely, the forming voltage used during anodic oxidation is generally from about 300 volts to about 380 volts, in some embodiments from about 320 volts to about 380 volts, and in some embodiments from about 340 to about 380 volts, and at temperatures ranging from about 25°C to about 50°C. While the exact mechanism is not fully understood, it is believed that such conditions can significantly improve the quality and thickness of the dielectric without compromising the uniformity and consistency of its surface coverage.

[0011] In addition to using anodic oxidation conditions that differ from those conventionally used, the solid electrolyte is also formed from a dispersion of preformed particles of conductive polymer. In this way, the electrolyte can generally remain free of high-energy radicals (e.g., Fe 2+ - or Fe3+ -ions), which can lead to degradation of the dielectric, especially at the ultra-high voltages mentioned above.

[0012] As a result of the present invention, the resulting capacitor can be used in ultra-high voltage applications. For example, the capacitor may have a relatively high "breakdown voltage" (voltage at which the capacitor fails), such as about 120 volts or more, in some embodiments about 175 volts or more, in some embodiments about 200 volts or more, and in some embodiments about 240 volts to about 300 volts. Similarly, the capacitor may also be capable of withstanding relatively high surge currents that are also commonly encountered in high voltage applications. The peak surge current may be, for example, about 100 amperes or more, in some embodiments about 200 amperes or more, and in some embodiments about 300 amperes to about 800 amperes.

[0013] Various embodiments of the present invention will now be described in greater detail. I. Anode

[0014] The anode is typically made from a valve metal composition. The specific charge of the composition can vary, such as from about 2,000 µF*V / g to about 70,000 µF*V / g, in some embodiments from about 3,000 µF*V / g to about 40,000 µF*V / g or more, and in some embodiments from about 4,000 µF*V / g to about 20,000 µF*V / g. The valve metal composition contains a valve metal (i.e., a metal that can be oxidized) or a valve metal-based compound, such as tantalum, niobium, aluminum, hafnium, titanium, alloys thereof, oxides thereof, nitrides thereof, and so on. For example, the valve metal composition may include an electrically conductive oxide of niobium, such as niobium oxide, having a niobium to oxygen atomic ratio of 1:1.0 ± 1.0, in some embodiments 1:1.0 ± 0.3, in some embodiments 1:1.0 ± 0.1, and in some embodiments 1:1.0 ± 0.05.For example, niobium oxide NbO. 0.7 , NbO 1.0 , NbO 1.1 and NbO 2 Examples of such valve metal oxides are described in US patents US 6,322,912 B1, US 6,391,275 B1, US 6,416,730 B1, US 6,527,937 B2, US 6,576,099 B2, US 6,592,740 B2, US 6,639,787 B2 and US 7,220,397 B2 as well as US patent applications US 2005 / 0 019 581 A1, US 2005 / 0 103 638 A1 and US 2005 / 0 013 765 A1.

[0015] To form the anode, a powder of the valve metal composition is generally used. The powder may contain particles of a variety of shapes, such as nodular, angular, flake, etc., as well as mixtures thereof. In particular embodiments, the particles may exhibit a flake-like morphology, having a relatively flat or platelet shape. Such particles may provide a short conduction line between the outer surface and the interior of the anode and also provide a highly continuous and dense wire-to-anode connection with high conductivity. Among other things, this may contribute to increasing the breakdown voltage (voltage at which the capacitor fails) and lowering the equivalent series resistance ("ESR"). The particles may also increase the specific charge of the anode when it is anodically oxidized at higher voltages, thereby increasing the energy density.

[0016] When used, the flake particles are generally flat. The degree of flatness is generally defined by the "shape factor," which is the average diameter or width of the particles divided by the average thickness ("D / d"). For example, the shape factor of the particles may be about 2 to about 100, in some embodiments about 3 to about 50, and in some embodiments about 4 to about 30. For example, the particles may have a specific surface area of ​​about 0.5 to about 10.0 m 2 / g, in some embodiments from about 0.7 to about 5.0 m 2 / g and in some embodiments from about 1.0 to about 4.0 m 2 / g. The term "specific surface area" generally refers to the surface area as determined by the physical gas adsorption (BET) method of Braunauer, Emmet and Teller, Journal of American Chemical Society, Vol. 60, 1938, p. 309, with nitrogen as the adsorbent gas. The test can be performed using a MONOSORB® Specific Surface Area Analyzer, available from QUANTACHROME Corporation, Syosset, NY, which measures the amount of adsorbate nitrogen gas adsorbed on a solid surface by detecting the change in thermal conductivity of a flowing mixture of adsorbate and inert carrier gas (e.g., helium).

[0017] Likewise, the mass density (also known as Scott density) typically ranges between about 0.1 and about 2 grams per cubic centimeter (g / cm 3 ), in some embodiments between about 0.2 g / cm 3 and about 1.5 g / cm 3and in some embodiments between about 0.4 g / cm 3 and about 1 g / cm 3 . "Bulk density" can be determined using a flow-through funnel and a density measuring cup. More specifically, the flake sample can be poured through the funnel into the cup until the sample completely fills the circumference of the cup and overflows, and then the sample can be scraped off with a spatula without jarring so that it is flush with the top of the cup. The scraped sample is transferred to a balance and weighed to the nearest 0.1 gram to determine the density value. Such a device is commercially available from Alcan Aluminum Corp. in Elizabeth, New Jersey. The particles can also have an average size (e.g., width) of about 0.1 to about 100 micrometers, in some embodiments from about 0.5 to about 70 micrometers, and in some embodiments from about 1 to about 50 micrometers.

[0018] To facilitate the construction of the anode, certain additional ingredients may also be included in the powder. For example, the powder may optionally be mixed with a binder and / or lubricant to ensure that the particles adhere properly to one another when pressed to form the anode body. Suitable binders may include, for example: polyvinyl butyral; polyvinyl acetate; polyvinyl alcohol; polyvinylpyrollidone; cellulosic polymers such as carboxymethylcellulose, methylcellulose, ethylcellulose, hydroxyethylcellulose, and methylhydroxyethylcellulose; atactic polypropylene, polyethylene; and polyethylene glycol (e.g., Carbowax from Dow Chemical Co.).); polystyrene, polybutadiene-styrene; polyamides, polyimides and polyacrylamides, high molecular weight polyethers; copolymers of ethylene oxide and propylene oxide; fluoropolymers such as polytetrafluoroethylene, polyvinylidene fluoride and fluoroolefin copolymers; acrylic polymers such as sodium polyacrylate, poly-lower alkyl acrylates, poly-lower alkyl methacrylates and copolymers of lower alkyl acrylates and lower alkyl methacrylates; and fatty acids and waxes such as stearic and other soapy fatty acids, vegetable wax and microwaxes (purified paraffins), etc. The binder may be dissolved and dispersed in a solvent. Exemplary solvents may include water, alcohols, and so on. When employed, the percentage of binders and / or lubricants may vary from about 0.1% to about 8% by weight of the total composition.However, it should be understood that binders and / or lubricants are not essential in the present invention.

[0019] The resulting powder can then be compacted using any conventional powder pressing device to form a pellet.

[0020] For example, a single-station compaction press containing a die and one or more punches may be used. Alternatively, anvil-type compaction presses may be used, which use only one die and a single lower punch. Single-station compaction presses are available in several basic types, such as cam, toggle, and eccentric / crank presses, with different features such as single-acting, double-acting, sliding die, moving platen, opposing piston, screw, impact, hot pressing, coining, or dimensional coining. The powder can be compacted around an anode lead wire. The wire can be made of any electrically conductive material, such as tantalum, niobium, aluminum, hafnium, titanium, etc., as well as their electrically conductive oxides or nitrides.

[0021] After densification, the resulting anode body can then be sliced ​​into any desired shape, such as square, rectangular, circular, oval, triangular, hexagonal, octagonal, heptagonal, pentagonal, etc. The anode body can also have a "grooved" shape containing one or more grooves, crevices, furrows, or indentations to increase the surface area to volume ratio and thereby minimize ESR and broaden the frequency response of the capacitance. The anode body can then be subjected to a heating step in which most, if not all, of the binder / lubricant is removed. For example, the anode body is typically heated by a furnace operating at a temperature between about 150°C to about 500°C. Alternatively, binders / solvent can also be removed by contacting the compact with an aqueous solution, such as in Bishop et al.granted US patent US 6 197 252 B1.

[0022] The compact is then sintered to form a porous, integral mass. The temperature, atmosphere, and time for sintering can depend on a variety of factors, such as the type of anode, the size of the anode, etc. Typically, sintering occurs at a temperature of about 800°C to about 1900°C, in some embodiments from about 1000°C to about 1500°C, and in some embodiments from about 1100°C to about 1400°C, for a time of between about 5 minutes and about 100 minutes, and in some embodiments between about 30 minutes and about 60 minutes. If desired, sintering can occur in an atmosphere that limits the transfer of oxygen atoms to the anode. For example, sintering can occur in a reducing atmosphere, such as a vacuum, inert gas, hydrogen, etc.The reducing atmosphere may have a pressure of about 10 Torr to about 2000 Torr, in some embodiments from about 100 Torr to about 1000 Torr, and in some embodiments from about 100 Torr to about 930 Torr. Mixtures of hydrogen and other gases (e.g., argon or nitrogen) may also be used.

[0023] The anode may also have a relatively low carbon and oxygen content. For example, the anode may have no more than about 50 ppm carbon, and in some embodiments, no more than about 10 ppm carbon. Similarly, the anode may have no more than about 0.15 ppm / µC / g oxygen, and in some embodiments, no more than about 0.10 ppm / µC / g oxygen. The oxygen content may be measured with a LECO Oxygen Analyzer and includes oxygen in the native oxide of the tantalum surface and bulk oxygen in the tantalum particles. The bulk oxygen content is controlled by the interval of the tantalum crystal lattice, which increases linearly with increasing oxygen content in tantalum until the solubility limit is reached. The method was described in "Critical Oxygen Content In Porous Anodes Of Solid Tantalum Capacitors," Pozdeev-Freeman et al., Journal of Materials Science: Materials In Electronics 9, (1998) 309-311, using X-ray diffraction analysis (XRDA) to measure the period of the tantalum crystal lattice. Oxygen in sintered tantalum anodes may be confined to thin natural surface oxide, while the bulk of the tantalum is virtually oxygen-free.

[0024] As noted above, an anode lead wire may also be connected to the anode body, extending in a longitudinal direction thereof. The anode lead wire may be in the form of a wire, sheet, etc., and may be formed from a valve metal compound, such as tantalum, niobium, niobium oxide, etc. The lead wire connection may be made using known techniques, such as by welding the lead wire to the body or embedding it in the anode body during formation (e.g., prior to compaction and / or sintering). II. Dielectric

[0025] To form the dielectric, the sintered anode is anodically oxidized (“anodized”) to form dielectric layer(s) over and / or within the anode. For example, a tantalum (Ta) anode can be anodized to tantalum pentoxide (Ta 2 O 5) are anodically oxidized. Anodic oxidation is carried out by initially bringing an electrolyte to the anode, such as by immersing the anode in a bath containing the electrolyte. The electrolyte is generally in the form of a liquid, such as a solution (e.g., aqueous or non-aqueous), a dispersion, a melt, etc. Generally, a solvent is used in the electrolyte, such as water (e.g., deionized water); ethers (e.g., diethyl ether and tetrahydrofuran); alcohols (e.g., methanol, ethanol, n-propanol, isopropanol, and butanol); triglycerides; ketones (e.g., acetone, methyl ethyl ketone, and methyl isobutyl ketone); esters (e.g., ethyl acetate, butyl acetate, diethylene glycol ether acetate, and methoxypropyl acetate); Amides (e.g. dimethylformamide, dimethylacetamide, dimethylcapryl / capric fatty acid amide and N-alkylpyrrolidones); nitriles (e.g. acetonitrile, propionitrile, butyronitrile and benzonitrile); Sulfoxides or sulfones (e.gDimethyl sulfoxide (DMSO) and sulfolane), and so on. The solvent can comprise between about 50 wt.% and about 99.9 wt.%, in some embodiments between about 75 wt.% and about 99 wt.%, and in some embodiments between about 80 wt.% and about 95 wt.% of the electrolyte. Although not strictly required, the use of an aqueous solvent (e.g., water) is often desirable to facilitate the formation of an oxide. Indeed, water can comprise about 1 wt.% or more, in some embodiments about 10 wt.% or more, in some embodiments about 50 wt.%, in some embodiments about 70 wt.% or more, and in some embodiments about 90 wt.% to 100 wt.% of the solvent(s) used in the electrolyte.

[0026] The electrolyte is electrically conductive and may have an electrical conductivity of about 1 millisiemens per centimeter ("mS / cm") or more, in some embodiments about 30 mS / cm or more, and in some embodiments between about 40 mS / cm and about 100 mS / cm, determined at a temperature of 25°C. To increase the electrical conductivity of the electrolyte, a compound capable of dissociating in the solvent to form ions may be used. Suitable ionic compounds for this purpose may include, for example, acids such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, polyphosphoric acid, boric acid, boronic acid, etc.; organic acids, including carboxylic acids, such as acrylic acid, methacrylic acid, malonic acid, succinic acid, salicylic acid, sulfosalicylic acid, adipic acid, maleic acid, malic acid, oleic acid, gallic acid, tartaric acid, citric acid, formic acid, acetic acid, glycolic acid, oxalic acid, propionic acid, phthalic acid, isophthalic acid, glutaric acid, gluconic acid, lactic acid, aspartic acid, glutamic acid, itaconic acid, trifluoroacetic acid, barbituric acid, cinnamic acid, benzoic acid, 4-hydroxybenzoic acid, aminobenzoic acid, etc.; sulfonic acids, such as methanesulfonic acid, benzenesulfonic acid, toluenesulfonic acid, trifluoromethanesulfonic acid, styrenesulfonic acid, naphthalenedisulfonic acid, hydroxybenzenesulfonic acid, dodecylsulfonic acid, dodecylbenzenesulfonic acid, etc.; polymeric acids, such as polyacrylic or polymethacrylic acid and their copolymers (e.g., maleic-acrylic, sulfonic-acrylic, and styrene-acrylic copolymers), carrageenic acid, carboxymethylcellulose, alginic acid, etc.; and so on.The concentration of ionic compounds is selected to achieve the desired electrical conductivity. For example, an acid (e.g., phosphoric acid) may comprise between about 0.01 wt.% and about 5 wt.%, in some embodiments between about 0.05 wt.% and about 0.8 wt.%, and in some embodiments between about 0.1 wt.% and about 0.5 wt.% of the electrolyte. If desired, mixtures of ionic compounds may also be used in the electrolyte.

[0027] A current is passed through the electrolyte to form the dielectric layer. The voltage value controls the charge (current multiplied by time) and thus the thickness of the dielectric layer. For example, the power supply can initially be set to a galvanostatic mode until the required voltage is reached. After that, the power supply is switched to a potentiostatic mode, where the voltage is kept constant to ensure that the desired thickness of dielectric forms on the anode surface. Of course, other known methods, such as pulsed methods, can also be used.In any event, as indicated above, the forming voltage used during anodic oxidation, which is typically equal to the peak voltage, is high, ranging from about 300 volts to about 380 volts, in some embodiments from about 320 volts to about 380 volts, and in some embodiments from about 340 to about 380 volts. During anodic oxidation, the electrolyte is also heated at a relatively low temperature within the range of about 25°C to about 50°C. III. Solid electrolyte

[0028] A solid electrolyte lies above the dielectric, which generally functions as the cathode of the capacitor. The solid electrolyte may be formed from one or more layers of conductive polymer. Regardless, the solid electrolyte generally contains a conductive polymer that is a substituted polythiophene. In one embodiment, the substituted polythiophene has, for example, the following general structure: where, TO or S; D is an optionally substituted C 1 - to C 5 -alkylene radical (e.g. methylene, ethylene, n-propylene, n-butylene, n-pentylene, etc.); R 7 a linear or branched, optionally substituted C 1 - to C 18-AlkylRadikal ist (z.B. Methyl, Ethyl, n- oder iso-Propyl, n-, iso-, sec- oder tert-Butyl, n-Pentyl, 1-Methylbutyl, 2-Methylbutyl, 3-Methylbutyl, 1-Ethylpropyl, 1,1-Dimethylpropyl, 1,2-Dimethylpropyl, 2,2-Dimethylpropyl, n-Hexyl, n-Heptyl, n-Octyl, 2-Ethylhexyl, n-Nonyl, n-Decyl, n-Undecyl, n-Dodecyl, n-Tridecyl, n-Tetradecyl, n-Hexadecyl, n-Octadecyl usw.); optional substituiertes C 5 - bis C 12 -Cycloalkyl-Radikal (z.B. Cyclopentyl, Cyclohexyl, Cycloheptyl, Cyclooctyl, Cyclononyl, Cyclodecyl usw.); optional substituiertes C e - bis C 14 -Aryl-Radikal (z.B. Phenyl, Naphthyl usw.); optional substituiertes C 7 - bis C 18 -Aralkyl-Radikal (z.B. Benzyl, o-, m-, p-Tolyl, 2,3-, 2,4-, 2,5-, 2-6, 3-4-, 3,5-Xylyl, Mesityl usw.); optional substituiertes C 1 - bis C 4 -Hydroxyalkyl-Radikal oder Hydroxyl-Radikal; und q is an integer from 0 to 8, in some embodiments from 0 to 2, and in one embodiment 0; and n is between 2 and 5,000, in some embodiments between 4 and 2,000, and in some embodiments between 5 and 1,000. Examples of substituents for the radicals "D" or "R 7 “ include, for example, cycloalkyl, aryl, aralkyl, alkoxy, halogen, ether, thioether, disulphide, sulfoxide, sulfone, sulfonate, amino, aldehyde, keto, carboxylic acid ester, carboxylic acid, carbonate, carboxylate, cyano, alkylsilane and alkoxysilane groups, carboxylamide groups and so on.

[0029] Particularly suitable thiophene polymers are those in which “D” is an optionally substituted C 2 - to C 3 -alkylene radical. For example, the polymer may be an optionally substituted poly(3,4-ethylenedioxythiophene) having the following general structure:

[0030] Methods for forming conductive polymers, such as those described above, are well known in the art. For example, US Patent No. 6,987,663 B2, which is incorporated herein by reference in its entirety for all purposes, describes various techniques for forming substituted polythiophenes from a monomeric precursor. The monomeric precursor may, for example, have the following structure: T, D, R 7 and q are defined above. Particularly suitable thiophene polymers are those in which “D” is an optionally substituted C 2 - to C 3 -alkylene radical. For example, optionally substituted 3,4-alkylenedioxythiophenes can be used, which have the following general structure: where R 7and q are as defined above. In a particular embodiment, "q" is 0. A commercially suitable example of 3,4-ethylenedioxythiophene is available from HC Starck GmbH under the designation Clevios™ M. Other suitable monomers are also described in US Patents US 5,111,327 A and US 6,635,729 B1, which are incorporated herein by reference in their entirety for all purposes. Derivatives of these monomers may also be used, which are, for example, dimers or trimers of the above monomers. Higher molecular weight derivatives, i.e., tetramers, pentamers, etc., of the monomers are suitable for use in the present invention. The derivatives may be prepared from identical or different monomer units and may be used in pure form and in admixture with each other and / or with the monomers. Oxidized or reduced forms of these precursors may also be used.

[0031] The thiophene monomers are chemically polymerized in the presence of an oxidative catalyst. The oxidative catalyst can be a transition metal salt, such as an inorganic or organic acid salt containing ammonium, sodium, gold, iron(III), copper(II), chromium(VI), cerium(IV), manganese(IV), manganese(VII), or ruthenium(III) cations. Particularly suitable transition metal salts include halides (e.g., FeCl 3 or HAuCl 4 ); salts of other organic acids (e.g. Fe(ClO 4 ) 3 , Fe 2 (SO 4 ) 3 , (NH 4 ) 2 S 2 O 8 or Na 3 Mon 12 PO 40 ); and salts of organic and inorganic acids comprising organic radicals. Examples of salts of inorganic acids with organic radicals include, for example, iron(III) salts of sulfuric acid monoesters of C 1 - to C 20-alkanols (e.g. iron(III) salt of lauryl sulfate). Likewise, examples of salts of organic acids include, for example, iron(III) salts of C 1 - to C 20 -Alkanesulfonic acids (e.g. methane, ethane, propanoic, butanoic or dodecanesulfonic acid); iron(III) salts of aliphatic perfluorosulfonic acids (e.g. trifluoromethanesulfonic acid, perfluorobutanesulfonic acid or perfluorooctanesulfonic acid); iron(III) salts of aliphatic C 1 - to C 20 -Carboxylic acids (e.g. 2-ethylhexylcarboxylic acid); iron(III) salts of aliphatic perfluorocarboxylic acids (e.g. trifluoroacetic acid or perfluorooctanoic acid); iron(III) salts of aromatic sulfonic acids, optionally substituted by C 1 - to C 20-alkyl groups (e.g., benzenesulfonic acid, o-toluenesulfonic acid, p-toluenesulfonic acid, or dodecylbenzenesulfonic acid); iron(III) salts of cycloalkanesulfonic acids (e.g., camphorsulfonic acid); and so on. Mixtures of these above-mentioned salts can also be used.

[0032] If necessary, the polymerization of the monomer can be carried out in a precursor solution. Solvents (e.g., polar, protic or non-polar) can be used in the solution, such as water, glycols (e.g., ethylene glycol, propylene glycol, butylene glycol, triethylene glycol, hexylene glycol, polyethylene glycols, ethoxydiglycol, dipropylene glycol, etc.); glycol ethers (e.g., methyl glycol ether, ethyl glycol ether, isopropyl glycol ether, etc.); alcohols (e.g., methanol, ethanol, n-propanol, isopropanol, and butanol); ketones (e.g., acetone, methyl ethyl ketone, and methyl isobutyl ketone); esters (e.g., ethyl acetate, butyl acetate, diethylene glycol ether acetate, methoxypropyl acetate, ethylene carbonate, propylene carbonate, etc.); amides (e.g., dimethylformamide, dimethylacetamide, dimethylcapryl / capric fatty acid amide, and N-alkylpyrrolidones). Sulfoxides or sulfones (e.g., dimethyl sulfoxide (DMSO) and sulfolane); phenolic compounds (e.g., toluene, xylene, etc.), and so on. Water is a particularly suitable solvent for the reaction.When used, the total amount of solvents in the precursor solution may be about 40 wt% to about 90 wt%, in some embodiments about 50 wt% to about 85 wt%, and in some embodiments about 60 wt% to about 80 wt%.

[0033] The polymerization of the thiophene monomer generally occurs at a temperature of about 10°C to about 100°C, and in some embodiments, from about 15°C to about 75°C. After the reaction is complete, known filtration techniques can be used to remove any salt impurities. One or more washing steps can also be used to refine the dispersion.

[0034] After polymerization, the resulting conductive polymer is generally in the form of small-sized particles, such as an average diameter of about 1 to about 200 nanometers, in some embodiments from about 2 to about 100 nanometers, and in some embodiments from about 4 to about 50 nanometers. The diameter of the particles can be determined using known techniques, such as ultracentrifuge, laser diffraction, etc. The shape of the particles can also vary. In a particular embodiment, for example, the particles have a spherical shape. However, it is understood that other shapes are also contemplated by the present invention, such as plates, rods, discs, bars, tubes, irregular shapes, etc.The concentration of particles in the dispersion can vary depending on the desired viscosity of the dispersion and the particular manner in which the dispersion is to be applied to the capacitor. Typically, however, the particles comprise between about 0.1 wt.% and about 10 wt.%, in some embodiments between about 0.4 wt.% and about 5 wt.%, and in some embodiments between about 0.5 wt.% and about 4 wt.% of the dispersion.

[0035] If desired, the formation of the conductive polymer into a particulate shape can be enhanced by using a separate counterion to counteract a charged conductive polymer (e.g., polythiophene). That is, the conductive polymer used in the solid electrolyte (e.g., polythiophene or a derivative thereof) has a charge on the main polymer chain that is neutral or positive (cationic). Polythiophene derivatives, for example, typically carry a positive charge in the main polymer chain. In some cases, the polymer may have positive and negative charges in the structural unit, with the positive charge located on the main chain and the negative charge optionally on the substituents of the "R" radical, such as sulfonate or carboxylate groups. The positive charges of the main chain may be partially or fully saturated with the optionally present anionic groups on the "R" radicals.Overall, the polythiophenes in these cases can be neutral or even anionic. Nevertheless, they are all considered cationic polythiophenes because the polythiophene backbone has a positive charge.

[0036] The counterion may be a monomeric or polymeric anion. Polymeric anions may be, for example, anions of polymeric carboxylic acids (e.g., polyacrylic acids, polymethacrylic acids, polymaleic acids, etc.); polymeric sulfonic acids (e.g., polystyrene sulfonic acids (“PSS”), polyvinyl sulfonic acids, etc.); and so on. The acids may also be copolymers, such as copolymers of vinylcarboxylic and vinylsulfonic acids with other polymerizable monomers, such as acrylic acid esters and styrene. Likewise, suitable monomeric anions include, for example, anions of C 1 - to C 20-alkanesulfonic acids (e.g. dodecanesulfonic acid); aliphatic perfluorosulfonic acids (e.g. trifluoromethanesulfonic acid, perfluorobutanesulfonic acid or perfluorooctanesulfonic acid); aliphatic C 1 - to C 20 -Carboxylic acids (e.g. 2-ethylhexylcarboxylic acid); aliphatic perfluorocarboxylic acids (e.g. trifluoroacetic acid or perfluorooctanoic acid); aromatic sulfonic acids, optionally substituted by C 1 -to C 20-Alkyl groups (e.g., benzenesulfonic acid, o-toluenesulfonic acid, p-toluenesulfonic acid, or dodecylbenzenesulfonic acid); cycloalkanesulfonic acids (e.g., camphorsulfonic acid or tetrafluoroborates, hexafluorophosphates, perchlorates, hexafluoroantimonates, hexafluoroarsenates, or hexachloroantimonates); and so on. Particularly suitable counterions are polymeric anions, such as polymeric carboxylic or sulfonic acid (e.g., polystyrenesulfonic acid ("PSS")). The molecular weight of such polymeric anions typically ranges from about 1,000 to about 2,000,000, and in some embodiments, from about 2,000 to about 500,000.

[0037] When employed, the weight ratio of such counterions to conductive polymers in a given layer of the solid electrolyte is typically between about 0.5:1 and about 50:1, in some embodiments between about 1:1 and about 30:1, and in some embodiments between about 2:1 and about 20:1. The weight of the electrically conductive polymers, based on the weight ratios given above, corresponds to the weighed portion of the monomers used, assuming that complete conversion occurs during polymerization.

[0038] In addition to conductive polymer(s) and optional counterion(s), the dispersion may also contain one or more binders to further enhance the adhesion of the polymer layer and also increase the stability of the particles in the dispersion. The binders may be organic, such as polyvinyl alcohols, polyvinylpyrrolidones, polyvinyl chlorides, polyvinyl acetates, polyvinyl butyrates, polyacrylic acid esters, polyacrylic acid amides, polymethacrylic acid esters, polymethacrylic acid amides, polyacrylonitriles, styrene / acrylic acid esters, vinyl acetate / acrylic acid esters, and ethylene / vinyl acetate copolymers, polybutadienes, polyisoprenes, polystyrenes, polyethers, polyesters, polycarbonates, polyurethanes, polyamides, polyimides, polysulfones, melamine-formaldehyde resins, epoxy resins, silicone resins, or celluloses. Crosslinking agents may also be used to increase the adhesiveness of the binder.Such crosslinking agents may include, for example: melamine compounds, masked isocyanates or functional silanes such as 3-glycidoxypropyltrialkoxysilane, tetraethoxysilane and tetraethoxysilane hydrolysate or crosslinkable polymers such as polyurethanes, polyacrylates or polyolefins, followed by crosslinking.

[0039] Dispersants can also be used to facilitate the formation of the solid electrolyte and the ability to apply it to the anode part. Suitable dispersants include solvents such as aliphatic alcohols (e.g., methanol, ethanol, i-propanol, and butanol), aliphatic ketones (e.g., acetone and methyl ethyl ketones), aliphatic carboxylic acid esters (e.g., ethyl acetate and butyl acetate), aromatic hydrocarbons (e.g., toluene and xylene), aliphatic hydrocarbons (e.g., hexane, heptane, and cyclohexane), chlorinated hydrocarbons (e.g., dichloromethane and dichloroethane), aliphatic nitriles (e.g., acetonitrile), aliphatic sulfoxides and sulfones (e.g., dimethyl sulfoxide and sulfolane), aliphatic carboxylic acid amides (e.g., methylacetamide, dimethylacetamide, and dimethylformamide), aliphatic and araliphatic ethers (e.g., diethyl ether and anisole), water, and mixtures of any of the foregoing solvents.A particularly suitable dispersant is water.

[0040] In addition to those mentioned above, other ingredients may also be used in the dispersion. For example, conventional fillers having a size of about 10 nanometers to about 100 micrometers, in some embodiments from about 50 nanometers to about 50 micrometers, and in some embodiments from about 100 nanometers to about 30 micrometers may be used. Examples of such fillers include calcium carbonate, silicates, silicon dioxide, calcium or barium sulfate, aluminum hydroxide, glass fibers or spheres, wood flour, cellulose powder, carbon black, electrically conductive polymers, etc. The fillers may be added to the dispersion in powder form, but may also be present in other forms, such as fibers.

[0041] Surfactants, such as ionic and non-ionic wetting agents, can also be used in the dispersion. Adhesives, such as organofunctional silanes or their hydrolysates, for example, 3-glycidoxypropyltrialkoxysilane, 3-aminopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, vinyltrimethoxysilane, or octyltriethoxysilane, can also be used. The dispersion may also contain additives that increase the conductivity, such as compounds containing ether groups (e.g. tetrahydrofuran), compounds containing lactone groups (e.g. γ-butyrolactone or γ-valerolactone), compounds containing amide or lactam groups (e.g. caprolactam, N-methylcaprolactam, N,N-dimethylacetamide, N-methylacetamide, N,N-dimethylformamide (DMF), N-methylformamide, N-methylformanilide, N-methylpyrrolidone (NMP), N-octylpyrrolidone or pyrrolidone), sulfones and sulfoxides (e.g.Sulfolane (tetramethylene sulfone) or dimethyl sulfoxide (DMSO)), sugars or sugar derivatives (e.g. sucrose, glucose, fructose or lactose), sugar alcohols (e.g. sorbitol or mannitol), furan derivatives (e.g. 2-furancarboxylic acid or 3-furancarboxylic acid) and alcohols (e.g. ethylene glycol, glycerol, di- or triethylene glycol).

[0042] The polymeric dispersion can be applied to the part using a variety of known techniques, such as spin coating, impregnation, pouring, dropwise application, injection, spraying, doctor blade coating, brushing, printing (e.g., inkjet, screen, or pad printing), or dipping. Although it may vary depending on the application technique used, the viscosity of the dispersion is typically about 0.1 to about 100,000 mPas (measured at a shear rate of 100 s -1), in some embodiments, about 1 to about 10,000 mPas, in some embodiments, about 10 to about 1,500 mPas, and in some embodiments, about 100 to about 1,000 mPas. After application, the layer can be dried and washed.

[0043] An advantage of using such a dispersion is that it may be able to penetrate into the edge region of the capacitor body to increase adhesion to the dielectric. This results in a mechanically more robust part, which can reduce the equivalent series resistance and leakage current. Such dispersions can also reduce the presence of ionic species (e.g., Fe 2+ or Fe 3+) that arise during in-situ polymerization, which can cause breakdown of the dielectric under high electric field strength due to ion migration. Thus, by applying the conductive polymer as a dispersion rather than by in-situ polymerization, the resulting capacitor can have a relatively high "breakdown voltage." If desired, the solid electrolyte can be formed from one or more layers. When multiple layers are used, it is possible for one or more of the layers to contain a conductive polymer formed by in-situ polymerization. However, if it is desired to achieve very high breakdown voltages, the present inventors have recognized that the solid electrolyte can be formed primarily from the polymeric dispersions described above and that it is generally free of conductive polymers formed via in-situ polymerization.Regardless of the number of layers used, the resulting solid electrolyte typically has a total thickness of about 1 micrometer (µm) to about 200 µm, in some embodiments from about 2 µm to about 50 µm, and in some embodiments from about 5 µm to about 30 µm.

[0044] The solid electrolyte can optionally be annealed after application to the anode part. Annealing can occur after each application of a solid electrolyte layer, or it can occur after the entire coating is applied if multiple layers are used. In some embodiments, the solid electrolyte can be annealed, for example, by immersing the compact in an electrolyte solution, such as an acid solution, and then applying a constant voltage to the solution until the current drops to a preselected level. If desired, this annealing can occur in multiple steps. After applying some or all of the layers described above, the resulting part can then be washed, if desired, to remove various byproducts, excess oxidants, and so on. Furthermore, in some cases, drying can be applied after some or all of the immersion steps described above.For example, drying may be desirable after application of the oxidizing agent and / or after washing the compact to open the pores of the part so that it can absorb a liquid during subsequent dipping steps. IV. Other components of the capacitor

[0045] If desired, the capacitor may also include other layers as known in the art. For example, a protective layer may optionally be formed between the dielectric and the solid electrolyte, such as a relatively insulating resin material (natural or synthetic). Such materials may have a resistivity of greater than about 10 Ω / cm, in some embodiments greater than about 100 Ω / cm, in some embodiments greater than about 1,000 Ω / cm, in some embodiments greater than about 1 × 10 5 Ω / cm and in some embodiments, greater than about 1 × 10 10Ω / cm. Some resinous materials that can be used in the present invention include, but are not limited to, polyurethane, polystyrene, esters of unsaturated or saturated fatty acids (e.g., glycerides), and so on. Suitable esters of fatty acids include, but are not limited to, esters of lauric acid, myristic acid, palmitic acid, stearic acid, eleostearic acid, oleic acid, linoleic acid, linolenic acid, aleuritic acid, shellolic acid, and so on. These fatty acid esters have been found to be particularly useful when used in relatively complex combinations to form a "drying oil" that allows the resulting film to quickly polymerize into a stable layer. Such drying oils can contain mono-, di-, and / or tri-glycerides, which have a glycerol backbone with one, two, or three fatty acid residues, respectively, that are esterified.Some suitable drying oils that may be used include, but are not limited to, olive oil, linseed oil, castor oil, tung oil, soybean oil, and shellac. These and other protective coating materials are described in more detail in U.S. Patent No. 6,674,635 B1, issued to Fife, et al., which is incorporated herein by reference in its entirety for all purposes.

[0046] If desired, a carbon layer (e.g., graphite) or a silver layer can also be applied to the part. The silver coating can serve, for example, as a solderable conductor, contact layer, and / or charge collector for the capacitor, and the carbon coating can limit the contact of the silver coating with the solid electrolyte. These coatings can partially or completely cover the solid electrolyte.

[0047] Terminals may also be provided on the capacitor, particularly when used in surface mount applications. For example, the capacitor may include an anode terminal to which the anode lead wire of the capacitor element is electrically connected, and a cathode terminal to which the cathode of the capacitor element is electrically connected. Any conductive material, such as a conductive metal (e.g., copper, nickel, silver, nickel, zinc, tin, palladium, lead, copper, aluminum, molybdenum, titanium, iron, zirconium, magnesium, and their alloys), may be used to form the terminals. Particularly suitable conductive metals include copper, copper alloys (e.g., copper-zirconium, copper-magnesium, copper-zinc, or copper-iron), nickel, and nickel alloys (e.g., nickel-iron). The thickness of the terminals is substantially selected to minimize the thickness of the capacitor.For example, the thickness of the leads may range from about 0.05 to about 1 millimeter, in some embodiments from about 0.05 to about 0.5 millimeters, and from about 0.07 to about 0.2 millimeters. An example of a conductive material is a metal plate made of a copper-iron alloy, available from Wieland (Germany). If desired, the surface of the leads may be electroplated with nickel, silver, gold, tin, etc., as known in the art, to ensure that the finished component can be mounted on a printed circuit board. In one specific embodiment, both surfaces of the leads are coated with nickel or flash silver, respectively, while the mounting surface is also coated with a layer of solder.

[0048] With reference to Fig.1, an embodiment of an electrolytic capacitor 30 is shown including an anode terminal 62 and a cathode terminal 72 in electrical communication with a capacitor element 33. The capacitor element 33 has a top surface 37, a bottom surface 39, a front surface 36, and a back surface 38. Although it may be in electrical contact with any of the surfaces of the capacitor element 33, in the illustrated embodiment, the cathode terminal 72 is in electrical contact with the bottom surface 39 and the back surface 38. More specifically, the cathode terminal 72 includes a first component 73 disposed substantially perpendicular to a second component 74. The first component 73 is in electrical contact and substantially parallel to the bottom surface 39 of the capacitor element 33. The second component 74 is in electrical contact and substantially parallel to the back surface 38 of the capacitor element 33.Although shown as one piece, it is understood that these sections may alternatively be separate parts connected to each other either directly or via an additional conductive element (e.g. metal).

[0049] The anode terminal 62 also includes a first component 63 disposed substantially perpendicular to a second component 64. The first component 63 is in electrical contact with and substantially parallel to the bottom surface 39 of the capacitor element 33. The second component 64 includes a region 51 supporting an anode lead wire 16. In the illustrated embodiment, the region 51 has a "U-shape" to further enhance surface contact and mechanical stability of the lead wire 16.

[0050] The terminals may be connected to the capacitor element using any technique known in the art. For example, in one embodiment, a lead frame may be provided that defines the cathode terminal 72 and the anode terminal 62. To attach the electrolytic capacitor element 33 to the lead frame, a conductive adhesive may first be applied to a surface of the cathode terminal 72. The conductive adhesive may, for example, include conductive metal particles embedded in a resin mixture. The metal particles may be silver, copper, gold, platinum, nickel, zinc, bismuth, etc. The resin mixture may include a thermosetting resin (e.g., epoxy resin), a hardener (e.g., acid anhydride), and a coupling agent (e.g., silane coupling agent). Suitable conductive adhesives are described in U.S. patent application Ser. No. 2006 / 0038304 A1, which Osako et al.and which is incorporated herein by reference in its entirety for all purposes. Any of a variety of methods may be used to apply the conductive adhesive to the cathode terminal 72. For example, printing techniques may be used for their practical and cost-saving advantages.

[0051] In general, a variety of methods can be used to attach the terminals to the capacitor. For example, in one embodiment, the second component 64 of the anode terminal 62 and the second component 74 of the cathode terminal 72 are first pushed upward into the Fig.1. The capacitor element 33 is then placed onto the cathode terminal 72 so that its lower surface 39 contacts the adhesive and the anode lead wire 16 is received in the lower U-shaped region 51. If desired, an insulating material (not shown), such as a plastic wafer or tape, may be placed between the lower surface 39 of the capacitor element 33 and the first component 63 of the anode terminal 62 to electrically insulate the anode and cathode terminals.

[0052] The anode wire 16 is then electrically connected to the lower portion 51 using any method known in the art, such as mechanical welding, laser welding, conductive adhesives, etc. For example, the anode wire 16 may be welded to the anode terminal 62 using a laser. Lasers generally include resonators containing a lasing medium capable of emitting photons by stimulated emission and an energy source that excites the elements of the lasing medium. One type of suitable laser is one in which the lasing medium consists of aluminum and yttrium garnet (YAG) doped with neodymium (Nd). The excited particles are neodymium ions, Nd. 3+The energy source can supply continuous energy to the laser medium to emit a continuous laser beam, or energy discharges to emit a pulsed laser beam. After the anode lead wire 16 is electrically connected to the anode terminal 62, the conductive adhesive can be cured. For example, a hot press can be used to apply heat and pressure to ensure that the electrolytic capacitor element 33 is sufficiently bonded to the cathode terminal 72 by the adhesive.

[0053] Once the capacitor element is attached, the lead frame is encased in a resin package, which can then be filled with silicon dioxide or any other known potting material. The width and length of the package can vary depending on the intended application. Suitable packages include packages "A", "B", "C", "D", "E", "F", "G", "H", "J", "K", "L", "M", "N", "P", "R", "S", "T", "V", "W", "X", "Y", or "Z" (AVX Corporation). Regardless of the package size used, the capacitor element is encapsulated in such a way that at least a portion of the anode and cathode terminals are exposed for mounting on a printed circuit board. As shown in Fig. 1, the capacitor element 33 is encapsulated in a housing 28 such that a portion of the anode terminal 62 and a portion of the cathode terminal 72 are exposed.

[0054] As a result of the present invention, the capacitor assembly may exhibit excellent electrical properties even when exposed to high-temperature environments. For example, the capacitor assembly may have an equivalent series resistance ("ESR") of less than about 50 ohms, in some embodiments less than about 25 ohms, in some embodiments from about 0.01 to about 10 ohms, and in some embodiments from about 0.05 to about 5 ohms, measured at an operating frequency of 100 Hz. Furthermore, leakage current, which generally refers to the current flowing from one conductor to the adjacent conductor through an insulator, may be maintained at relatively low levels.For example, the numerical value of the normalized leakage current of a capacitor according to the present invention is, in some embodiments, less than about 1 µA / µF*V, in some embodiments, less than about 0.5 µA / µF*V, and in some embodiments, less than about 0.1 µA / µF*V, where µA represents microamperes and µF*V is the product of the capacitance and the voltage rating. Such values ​​for ESR and normalized leakage current can be maintained even after aging for a significant period of time at high temperatures. For example, the values ​​can be maintained for 100 hours or more, in some embodiments, between about 300 hours and about 3000 hours, and in some embodiments, between about 400 hours and about 2500 hours (e.g.,500 hours, 600 hours, 700 hours, 800 hours, 900 hours, 1000 hours, 1100 hours, 1200 hours, or 2000 hours) at temperatures ranging from about 50°C to about 250°C, in some embodiments from about 70°C to about 225°C, and in some embodiments from about 100°C to about 225°C (e.g., 100°C, 125°C, 150°C, 175°C, or 200°C).

[0055] The capacitor can also have a high energy density, making it suitable for use in high-pulse applications. Energy density is generally defined according to the equation E=1 / 2*CV 2where C is the capacitance in farads (F) and V is the working voltage of the capacitor in volts (V). The capacitance can be measured, for example, using a capacitance meter (e.g., Keithley 3330 precision LCZ meter with Kelvin leads, 2 volt bias, and 1 volt signal) at an operating frequency of 120 Hz and a temperature of 25 °C. For example, the capacitor can have an energy density of approximately 2.0 joules per cubic centimeter (J / cm 3 ) or more, in some embodiments approximately 3.0 J / cm 3 , in some embodiments of approximately 4.0 J / cm 3 up to approximately 10.0 J / cm 3 , and in some embodiments of approximately 4.5 J / cm 3 up to approximately 8.0 J / cm 3 . The specific capacitance can be approximately 1 millifarad per square centimeter (“mF / cm 2 “) or more, in some embodiments approximately 2 mF / cm 2or more, in some embodiments about 5 to about 50 mF / cm 2 and in some embodiments, about 8 to about 20 mF / cm 2 be.

[0056] The present invention can be better understood by reference to the following examples. Test procedureCapacity

[0057] The capacitance was measured using a Keithley 3330 precision LCZ meter with Kelvin leads at 2.2 volts DC bias and a sine wave of 0.5 volts peak-to-peak. Equivalent series resistance (ESR)

[0058] The equivalent series resistance can be measured using a Keithley 3330 precision LCZ meter with Kelvin leads at a 2.2 V DC bias and a 0.5 V peak-to-peak sine wave. The operating frequency was 100 Hz, and the temperature was at room temperature. Leakage current:

[0059] The leakage current (“DCL”) was measured using a leakage current test device that measures the leakage current at room temperature and rated voltage after at least 60 seconds. Surge current:

[0060] The surge current test was conducted at room temperature according to an article entitled "Surge in Solid Tantalum Capacitors" by John Gill, which is included here in its entirety for all purposes as a reference. In particular, the surge current test was carried out using the circuit according to Fig. 2 carried out: The test sequence generally runs as follows: (a) A single capacitor is charged up to the voltage at which the capacitor is short-circuited (starting at the rated voltage). (b) The test probes are lowered onto the capacitor. The switching FET is off at this stage, so no current flows. (c) The FET is turned on, allowing a fast, instantaneous peak current to flow and charge the capacitor. The peak current is equivalent to ~2x the part's voltage rating. For example, a capacitor with a voltage rating of 50 volts has a peak current of about 100 amperes. (d) The current is monitored through a resistor (e.g., a 0.18 ohm resistor) in the source line of the transistor, and the part is dynamically discarded if its current still does not decrease after a predetermined time based on capacitance. (e) The FET is turned off to stop the charging process; and (f) previous voltage and current before the capacitor shorted are recorded. Breakdown voltage:

[0061] The breakdown voltage test was conducted at room temperature. The test was performed by charging a single capacitor with 0.01 mA across a 10 kOhm resistor (charge slope dU / dt=1). If the applied voltage decreased by more than 10%, the breakdown voltage value was recorded. EXAMPLE 1

[0062] Tantalum powder with 9000 µFV / g was used to form anode samples. A tantalum wire was embedded in each anode sample, sintered at 1800 °C, and heated to a density of 5.3 g / cm 3pressed. The resulting compacts had a size of 5.00 x 3.70 x 2.00 mm. The compacts were anodically oxidized to 300 V in a water / ethylene glycol / phosphoric acid electrolyte with a conductivity of 2.9 mS at a temperature of 45 °C to form the dielectric layer. A conductive polymer coating was then formed by dipping the anode into a dispersed poly(3,4-ethylenedioxythiophene) with a solids content of 1.1% (Clevios™ K, HC Starck). After coating, the part was then dried at 125 °C for 20 minutes. This process was repeated 6 times. The part was then dipped into a dispersed poly(3,4-ethylenedioxythiophene) with a solids content of 2% and dried at 125 °C for 20 minutes. The parts were then dipped in a graphite dispersion and dried. Finally, the parts were dipped in a silver dispersion and dried.The finished parts were assembled using conventional assembly techniques. Multiples (1,000) of 3.3 µF / 125 V capacitors were manufactured in this way. EXAMPLE 2 - not in accordance with the claim

[0063] Tantalum powder with 9000 µFV / g was used to form anode samples. A tantalum wire was embedded in each anode sample, sintered at 1800 °C, and heated to a density of 5.3 g / cm 3pressed. The resulting compacts measured 5.00 x 3.70 x 2.00 mm. The compacts were anodically oxidized to 300 V in a water / ethylene glycol / phosphoric acid electrolyte with a conductivity of 2.9 mS at a temperature of 85 °C to form the dielectric layer. A conductive polymer coating, graphite coating, silver coating, and assembly process were performed in the same manner as described above. Multiples (1,000) of 3.3 µF / 125 V capacitors were fabricated in this manner.

[0064] The finished parts of Examples 1 and 2 were then tested for their electrical performance (i.e., capacitance ("CAP"), equivalent series resistance ("ESR"), and leakage current ("DCL")). The average results are presented below. Pattern CAP (µF) ESR (Ω) DCL (µA) Example 1 3,57 0,142 0,1 Example 2 3,61 0,132 0,1

[0065] The finished parts of Examples 1 and 2 were also tested for breakdown voltage. The parts passed the test if the breakdown voltage (BDV) was higher than 1.3 U N and then 1.6 U N (higher than 162.5 V in cases of Examples 1 and 2). The results are given below. Pattern BDV > 162.5 V [%] BDV > 200 V [%] Example 1 94,2 82,3 Example 2 58,6 41,8

[0066] 100 finished parts of Example 1 and 100 finished parts of Example 2 were also tested for surge current. The average results are shown below. Pattern U max (V) I max (Amp) Example 1 185,5 456 Example 2 156,9 355

[0067] As indicated, the capacitor assemblies of Example 2, which contained anodes anodized at a temperature of 85 °C, were less stable under surge current conditions than the assemblies used in Example 1, which contained anodes anodized at a temperature of 45 °C.

Claims

[1] A method of forming an ultra-high voltage solid electrolytic capacitor element (33), the method comprising: anodically oxidizing a sintered porous anode body at a forming voltage of 300 volts to 380 volts and a temperature of 25°C to 50°C to form an anode including a dielectric coating on the anode body, the anode body being formed from a powder containing tantalum, niobium, or an electrically conductive oxide thereof; and Applying a dispersion of conductive polymer particles to the anode to form a solid electrolyte, wherein the conductive polymer particles contain a substituted polythiophene. [2] The method of claim 1, wherein the porous anode body is immersed in a bath containing an electrolyte, the electrolyte being maintained at a temperature between 25°C and 50°C. [3] The method of claim 2, wherein a current is passed through the electrolyte to form the dielectric coating at a voltage of 300 volts to 380 volts. [4] A method according to any one of the preceding claims, wherein the forming voltage is between 340 volts and 380 volts. [5] A method according to any one of the preceding claims, wherein the porous anode body is formed from a tantalum powder containing flake particles having an aspect ratio of 2 to 100. [6] A method according to any one of the preceding claims, wherein the porous anode body is formed from a powder having a specific charge of 5,000 to 40,000 µF*V / g. [7] A process according to any one of the preceding claims, wherein the substituted polythiophene has the following general structure:wherein TO or S; D is an optionally substituted C 1 - to C 5-alkylene radical; R 7 a linear or branched, optionally substituted C 1 - to C 18 -alkyl radical; optionally substituted C 5 - to C 12 -cycloalkyl radical; optionally substituted C 6 - to C 14 -aryl radical; optionally substituted C 7 -to C 18 -Aralkyl radical; optionally substituted C 1 - to C 4 -hydroxyalkyl radical or hydroxyl radical; q is an integer from 0 to 8; and n is 2 to 5 000. [8] A process according to any one of the preceding claims, wherein the substituted polythiophene has the following general structure: wherein R 7 a linear or branched, optionally substituted C 1 - to C 18 -alkyl radical; optionally substituted C 6 - to C 14 -aryl radical; optionally substituted C 1 - to C 4-hydroxyalkyl radical or hydroxyl radical; q is an integer from 0 to 8; and n is 2 to 5 000. [9] A method according to any one of the preceding claims, wherein the conductive polymer particles comprise poly(3,4-ethylenedioxythiophene) or a derivative thereof. [10] A method according to any one of the preceding claims, wherein the conductive polymer particles have an average diameter of 1 to 200 nanometers. [11] A method according to any one of the preceding claims, wherein the solid electrolyte further comprises a counter ion. [12] A process according to the preceding claim, wherein the counterion is a monomeric or polymeric anion. [13] A method according to any one of the preceding claims, further comprising a lead wire (13) extending in a longitudinal direction from the porous body of the anode. [14] A method according to any one of the preceding claims, wherein the solid electrolyte is generally free of conductive polymers formed by in-situ polymerization.

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