Solid electrolytic capacitor with improved high voltage properties

Abstract

Solid electrolytic capacitor comprising: a sintered porous anode formed from a finely divided powder having a specific charge of more than about 30,000 µF*V / g, the powder containing particles having a three-dimensional shape; a dielectric layer covering the anode body; and a solid electrolyte covering the dielectric layer, the solid electrolyte comprising a layer comprising a plurality of prepolymerized conductive polymer particles and further comprising a layer of hydroxy-functional nonionic copolymer substantially free of conductive polymer; wherein the capacitor has a breakdown voltage of about 60 V or more.

Description

BACKGROUND OF THE INVENTIONSolid electrolytic capacitors (e.g., tantalum capacitors) are typically formed by pressing a metal powder (e.g., tantalum) around a metal lead wire, sintering the pressed portion, anodizing the sintered anode, and then applying a solid electrolyte. When high voltages are expected, such as occur during rapid turn-on or operating current spikes, it is generally necessary to employ only certain types of materials in the capacitor design. For example, the anode of conventional high voltage capacitors is formed from a flake powder having a specific charge typically in the range of about 10000 to about 15000 μF*V / g. Unfortunately, such materials also have a relatively low specific surface area, which greatly limits the capacitance that can be achieved. Therefore, there is a need at present for a solid electrolytic capacitor having improved characteristics in high voltage environments.US 2012 / 0 106 031 A1 discloses a capacitor for high-voltage and high-temperature inserts. It comprises an anode, a dielectric and a solid electrolyte of conductive polymer particles free of harmful radicals (e.g. Fe 2+, Fe 3+) in order to avoid degradation at voltages above 60 volts. The capacitor is hermetically enclosed in a housing with inactive gas, which reduces access of oxygen and moisture and increases thermal stability. As a result, it is suitable for high voltages, temperatures and high volume efficiency.DE 10 2007 048 212 A1 discloses a method for producing electrolytic capacitors having a low equivalent series resistance and low residual current. These capacitors consist of a solid electrolyte, an intermediate layer and an outer layer containing conductive polymers. The invention also encompasses the electrolytic capacitors produced by this process and their possible uses.Brief Description of the InventionAccording to an embodiment of the present invention, a solid electrolytic capacitor is disclosed that includes a sintered porous anode, a dielectric layer covering the anode body, and a solid electrolyte covering the dielectric layer. The anode is formed from a particulate powder having a specific charge of greater than about 30000 μF*V / g, and the powder contains particles having a three-dimensional shape. The solid electrolyte is a layer comprising a plurality of prepolymerized conductive polymer particles and further a layer of hydroxyfunctional nonionic copolymer substantially free of conductive polymer. The capacitor has a breakdown voltage of about 60 V or more.According to another embodiment of the present invention, a method of forming a solid electrolytic capacitor is disclosed. The method comprises pressing a particulate powder into the form of a compact, the powder having a specific charge greater than about 30000 μF*V / g and containing particles having a three-dimensional shape; sintering the compact; anodizing the sintered compact to form a dielectric layer covering the anode; and applying a dispersion of prepolymerized conductive polymer particles to the dielectric layer and further applying a hydroxy-functional nonionic copolymer substantially free of conductive polymer.Further features and aspects of the present invention are set forth in more detail below.Brief Description of the DrawingsThroughout the remainder of the specification and with reference to the accompanying drawings, a complete and remanufacturable disclosure of the present invention, including its best mode of realization, is set forth in particular by those skilled in the art; in which: FIG. 1 is a schematic illustration of an embodiment of a capacitor that may be formed in accordance with the present invention.Where reference numerals are used in the present specification and drawings in multiple numbers, they are intended to represent the same or analogous features or elements of the present invention.DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENTSGenerally speaking, the present invention relates to a solid electrolytic capacitor comprising a sintered porous anode, a dielectric layer covering the anode, and a solid electrolyte covering the dielectric layer. The anode is formed from a particulate powder (e.g., spheroidal or angular) having a relatively high specific charge, such as greater than about 30,000 microfarads*Volt per gram ("μF*V / g"), in some embodiments about 32000 to about 80,000 μF*V / g, in some embodiments about 33000 to about 60000 μF*V / g, and in some embodiments about 35000 to about 45,000 μF*V / g. As is known in the art, the specific charge can be determined by multiplying the capacitance by the anodizing voltage employed and then dividing the product by the weight of the anodized electrode body. The fine powder also contains primary particles having a three-dimensional shape such as a spheroidal or angular shape. Such particles are not substantially flat, and thus have a relatively low "aspect ratio", which is the average diameter or width of the particles divided by the average thickness ("D / T"). For example, the aspect ratio of the particles may be about 4 or less, in some embodiments about 3 or less, and in some embodiments about 1 to about 2.Despite the use of powders with such a high specific charge and with three-dimensional particles, the inventors have nevertheless found that the ability to achieve high voltages can be achieved by a unique and targeted combination of features relating to the formation of the anode and the solid electrolyte. In particular, relatively high press densities and sintering temperatures may be used to achieve relatively large "sintering bridges" between adjacent agglomerated particles. Sintered bridges are the small cross-sectional area of the current path within the metal structure. Typically, the sinter bridges have a size of about 200 nanometers or more, in some embodiments about 250 nanometers or more, and in some embodiments about 300 to about 800 nanometers. Because the bridges are relatively large, the dielectric layer near the bridge is more likely not to fail at high forming voltages. In addition to the anode, the manner in which the solid electrolyte is formed is also helpful in order for the resulting capacitor to operate at high voltages, namely the solid electrolyte is formed from a plurality of prepolymerized conductive polymer particles. Such particles may minimize the use of high energy radicals (e.g., Fe 2+- or Fe 3+- ions) that may otherwise result in degradation of the dielectric, particularly at the high voltages mentioned above.Thus, as a result of the present invention, the resulting capacitor can be used in high voltage applications such as rated voltages of about 35 volts or more, in some embodiments about 50 volts or more, and in some embodiments about 60 volts to about 200 volts. The capacitor may have, for example, a relatively high "breakdown voltage" (voltage at which the capacitor fails), such as about 60 volts or more, in some embodiments about 70 volts or more, in some embodiments about 80 volts or more, and in some embodiments about 100 volts to about 300 volts. Likewise, the capacitor may also be capable of withstanding relatively high surge currents that also frequently occur 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.Various embodiments of the present invention will now be described in more detail.I. AnodeTo form the anode, a finely divided powder of a valve metal composition is used. The valve metal composition generally includes a valve metal (i.e., a metal capable of oxidation) or a compound based on a valve metal, such as tantalum, niobium, aluminum, hafnium, titanium, alloys thereof, oxides thereof, nitrides thereof, etc. For example, the valve metal composition may include an electrically conductive oxide of niobium, such as a niobium oxide having an atomic ratio of niobium to oxygen 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. The niobium oxide may be NbO 0,7, NbO 1,0, NbO 1,1 and NbO 2. Examples of such valve metal oxides are described in U.S. Pat. Nos. 6,322,912 B1 (Fife), 6,391,275 B1 (Fife et al.), 6,416,730 B1 (Fife et al.), 6,527,937 B2 (Fife), 6,576,099 B2 (Kimmel et al.), 6,592,740 B2 (Fife et al.) and 6,639,787 B2 (Kimmel et al.) and U.S. Pat. No. 7,220,397 B2 (Kimmel et al.), as well as in U.S. Pat. Nos. 2005 / 0 019 581 A1 (Schneider), which are hereby incorporated by reference in their entirety by reference herein in their entireties, US 2005 / 0 103 638 A1 (Schneider et al.) and US 2005 / 0 013 765 A1 (Thomas et al.). The particles may also have a specific surface area of about 0.5 to about 10.0 m 2 / g, in some embodiments about 0.7 to about 5.0 m 2 / g, and in some embodiments about 1.0 to about 4.0 m 2 / g. The term "specific surface area" refers generally to the surface area determined by the Brunauer, Emmett and Teller Physical Gas Adsorption (B.E.T.) method, Journal of American Chemical Society, Vol. 60, 1938, p.309, with nitrogen as the adsorbing gas. The test can be performed with a MONOSORB ® Specific Surface Area Analyzer available from QUANTACHROME Corporation of Syosset, NY, which measures the amount of the adsorbable nitrogen gas adsorbed on a solid surface by reacting to the change in thermal conductivity of a flowing mixture of adsorbate and inert carrier gas (e.g., helium). Bulk density (also known as Scott density) is also typically about 0.1 to about 2 grams per cubic centimeter (g / cm 3), in some embodiments about 0.2 g / cm 3 to about 1.5 g / cm 3 and in some embodiments about 0.4 g / cm 3 to about 1 g / cm 3. The "bulk density" can be determined using a trickle measuring funnel and a density beaker. In particular, the flake sample can be poured into the cup through the funnel until the sample completely fills the cup and runs over the rim of the cup, and thereafter the sample can be flattened with a spatula without shaking so that it just closes off the top of the cup. The blotted sample is transferred to a scale and weighed to the accuracy of 0.1 gram to determine the density value. Such apparatus is commercially available from the Alcan Aluminum Corp. of Elizabeth, New Jersey. In certain embodiments, the particles may also have an average size of about 20 to about 250 micrometers, in some embodiments about 30 to about 150 micrometers, and in some embodiments about 40 to about 100 micrometers.Various other conventional treatments may also be used in the present invention to improve the properties of the powder. For example, in certain embodiments, the powder may be doped with sintering retarders in the presence of a dopant, such as aqueous acids (e.g., phosphoric acid). The amount of dopant added depends in part on the specific surface area of the powder, but typically it is present in an amount of no more than about 200 ppm. The dopant may be added before, during and / or after any heat treatment steps. The powder may also be subjected to one or more deoxidation treatments to improve ductility and reduce leakage current in the anodes. For example, the powder may be exposed to a getter material (e.g., magnesium) as described in U.S. Patent No. 4,960,471. The getter material may be present in an amount of about 2 to about 6 wt%. The temperature at which the deoxidation occurs may vary, but is typically in the range of about 700° C. to about 1600° C., in some embodiments about 750° C. to about 1200° C., and in some embodiments about 800° C. to about 1000° C. The total time of the deoxidation treatment(s) may be in the range of about 20 minutes to about 3 hours. The deoxidation is also preferably carried out in an inert atmosphere (e.g., argon). After the deoxidation treatment(s) is completed, the magnesium or other getter material typically vaporizes and forms a precipitate on the cold wall of the furnace. However, in order to ensure removal of the getter material, the fine agglomerates and / or coarse agglomerates may also be subjected to one or more acid treatment steps, such as with nitric acid, hydrofluoric acid, etc.To facilitate the construction of the anode, certain additional components can also be incorporated into the powder. For example, the powder may optionally be mixed with a binder and / or lubricant to ensure that the particles adhere sufficiently to each other when pressed to form the anode body. Suitable binders include, for example, polyvinyl butyral, polyvinyl acetate, polyvinyl alcohol, polyvinyl pyrrolidone, cellulose polymers such as carboxymethylcellulose, methylcellulose, ethylcellulose, hydroxyethylcellulose and methylhydroxyethylcellulose, atactic polypropylene, polyethylene, polyethylene glycol (e.g., Carbowax from Dow Chemical Co.), polystyrene, poly(butadiene / 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 methacrylates; The binder can be dissolved and dispersed in a solvent. Exemplary solvents are such as water, alcohols, etc. When used, the percentage of binders and / or lubricants may vary from about 0.1 to about 8% by weight of the total mass. However, it should be understood that binders and lubricants are not necessarily required in the present invention.The resulting powder can be compacted to form a compact by any conventional powder compacting apparatus. For example, a die may be used which is a single-place compacting press containing a die and one or more punches. Alternatively, anvil-type compacting dies using only one die and a single sub punch may be used. Single-site compacting dies are available in several basic types, such as cam, toggle and eccentric or crank presses with different capabilities, such as single-action, double-action, floating shell die, movable die clamping plate, counter punch, worm, impact, hot pressing, stamping or sizing. The powder may be compacted around an anode lead wire. The wire may be formed of any electrically conductive material such as tantalum, niobium, aluminum, hafnium, titanium, etc., as well as electrically conductive oxides thereof and / or nitrides thereof. After compaction, the resulting anode body may then be cut into any desired shape, such as square, rectangular, circular, oval, triangular, hexagonal, octagonal, seven corner, pentagonal, etc. The anode may also have a "corrugated" shape by including one or more grooves, grooves, depressions, or indentations to increase the surface area to volume ratio and thereby minimize ESR and extend the capacitance frequency response. The anode body may then be subjected to a heating step in which most, if not all, of a binder / lubricant, if any, is removed. For example, the anode body is typically heated in a furnace operating at a temperature of about 150° C. to about 500° C. Alternatively, the binder / lubricant can also be removed by contacting the compact with an aqueous solution as described in U.S. Pat. No. 6,197,252 B1 (Bishop et al.).Thereafter, the compact is sintered to form a porous integral mass. As mentioned above, it is believed that the use of relatively high sintering temperatures and press densities helps to achieve relatively large "sintering bridges" between the particles, which can improve the ability of the resulting dielectric to withstand high stresses. Here, the sintering temperature is typically in a range from about 1300° C. to about 1800° C., in some embodiments from about 1350° C. to about 1600° C., and in some embodiments from about 1400° C. to about 1500° C. Likewise, the press density may be in a range from about 4.5 to about 7.0 grams per cubic centimeter, in some embodiments from about 5.0 to about 6.5, and in some embodiments from about 5.0 to about 6.0 grams per cubic centimeter. The press density is determined by dividing the amount of powder (before sintering) by the volume of the compact (before sintering).The resulting sintered 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 about 2000 to about 10000 ppm oxygen, in some embodiments about 2500 to about 6000 ppm oxygen, and in some embodiments about 3000 to about 5000 ppm oxygen. The oxygen content can be measured with a LECO oxygen analyzer and comprises oxygen in natural oxide on the tantalum surface and volume oxygen within the tantalum particles. The volume oxygen content is controlled by the crystal lattice spacing of the tantalum, which increases linearly with increasing oxygen content in the tantalum until the solubility limit is reached. This 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 crystal lattice spacing of tantalum. The oxygen in sintered tantalum anodes can be limited to thin natural surface oxide while the volume of tantalum is substantially free of oxygen.As mentioned above, an anode terminal extending in the longitudinal direction may also be fixed to the anode body. The anode terminal may be in the form of a wire, sheet metal, etc., and may be made of a valve metal compound such as tantalum, niobium, niobium oxide, etc. Attachment of the terminal may be accomplished using known techniques, such as welding the terminal to the body or embedding within the anode body during formation (e.g., prior to compaction and / or sintering).Dielectric IIThe anode is also coated with a dielectric. The dielectric may be formed by anodizing ("anodizing") the sintered anode to form a dielectric layer on and / or within the anode. For example, an anode of tantalum (Ta) may be anodized to tantalum pentoxide (Ta 2 O 5). Typically, the anodization is carried out by first applying a solution to the anode, for example by immersing the anode in the electrolyte. Generally, a solvent such as water (e.g., deionized water) is used. In order to enhance the ionic conductivity, a compound capable of dissociation in the solvent to form ions may be used. Examples of such compounds are, for example, acids as described below with reference to the electrolyte. For example, an acid (e.g., phosphoric acid) may constitute about 0.01 wt % to about 5 wt %, in some embodiments about 0.05 wt % to about 0.8 wt %, and in some embodiments about 0.1 wt % to about 0.5 wt % of the anodizing solution. If desired, mixtures of acids may also be employed.A current is passed through the anodizing solution to form the dielectric layer. The value of the forming voltage corresponds to the thickness of the dielectric layer. For example, the power source may be first operated in galvanostatic mode until the required voltage is reached. Thereafter, the current source may be switched to a potentiostatic mode to ensure that the desired thickness of dielectric is formed over the entire surface of the anode. Of course, other known methods can also be used, such as potentiostatic pulse or step methods. The voltage at which the anodic oxidation occurs is typically in the range of about 4 to about 250 V, and in some embodiments about 9 to about 200 V, and in some embodiments about 20 to about 150 V. During the oxidation, the anodizing solution may be maintained at an elevated temperature, such as about 30° C. or more, in some embodiments about 40° C. to about 200° C., and in some embodiments about 50° C. to about 100° C. The anodic oxidation may also be performed at ambient temperature or below. The resulting dielectric layer may be formed on a surface of the anode and within its pores.Although not required, in certain embodiments, the dielectric layer may have a different thickness over the entire anode in that it has a first portion covering an outer surface of the anode and a second portion covering an inner surface of the anode. In such embodiments, the first part is selectively shaped such that its thickness is greater than that of the second part. However, it should be understood that the thickness of the dielectric layer need not be uniform within a certain range. For example, certain portions of the dielectric layer adjacent the outer surface may actually be thinner than certain portions of the layer on the inner surface, and vice versa. However, the dielectric layer may be formed such that at least a part of the layer on the outer surface has a greater thickness than at least a part on the inner surface. Although the exact difference in these thicknesses may vary depending on the particular application, the ratio of the thickness of the first portion to the thickness of the second portion is typically about 1.2 to about 40, in some embodiments about 1.5 to about 25, and in some embodiments about 2 to about 20.To form a dielectric layer having a different thickness, a multistage process is generally used. At each stage of the process, the sintered anode is anodized ("anodized") to form a dielectric layer (e.g., tantalum pentoxide). During the first stage of anodization, a relatively small forming voltage is typically used to ensure that the desired thickness of the dielectric for the inner region is achieved, such as forming voltages in the range of about 1 to about 90 volts, in some embodiments about 2 to about 50 volts, and in some embodiments about 5 to about 20 volts. Thereafter, the sintered body may then be anodized at a second stage of the process to increase the thickness of the dielectric to the desired level. This is generally accomplished by anodizing in an electrolyte at a higher voltage than was used during the first stage, such as at forming voltages in the range of about 50 to about 350 volts, in some embodiments about 60 to about 300 volts, and in some embodiments about 70 to about 200 volts. During the first and / or second stages, the electrolyte may be maintained at a temperature in the range of about 15° C. to about 95° C., in some embodiments about 20° C. to about 90° C., and in some embodiments about 25° C. to about 85° C.The electrolytes used during the first and second stages of the anodization process may be the same or different. Typically, however, it is desirable to employ various solutions to facilitate achieving greater thickness at the outer portions of the dielectric layer. For example, it may be desirable that the electrolyte used in the second stage has a lower ionic conductivity than the electrolyte used in the first stage to prevent a significant amount of oxide layer from forming on the inner surface of the anode. In this regard, the electrolyte used during the first stage may contain an acidic compound such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, polyphosphoric acid, boric acid, boronic acid, etc. Such an electrolyte may have an electrical conductivity of about 0.1 to about 100 mS / cm, in some embodiments about 0.2 to about 20 mS / cm, and in some embodiments about 1 to about 10 mS / cm, determined at a temperature of 25° C. The electrolyte employed during the second stage typically contains a salt of a weak acid such that the hydronium ion concentration in the pores increases as a result of a charge pass therein. Ion transport or diffusion takes place such that the anion of the weak acid moves into the pores according to the need to balance the electric charges. As a result, the concentration of the principal conductive species (hydronium ion) is reduced in establishing equilibrium between the hydronium ion, the acid anion and the undissociated acid, and thereby a less conductive species is formed. The reduction in the concentration of the conductive species results in a relatively high voltage drop in the electrolyte, which hinders the further anodization in the interior, while a thicker oxide layer is built up on the outside up to a higher forming voltage in the region of the continued high conductivity. Suitable salts of weak acids include, for example, ammonium or alkali metal salts (e.g., sodium, potassium, etc.) of boric acid, boronic acid, acetic acid, oxalic acid, lactic acid, adipic acid, etc. Particularly suitable salts are sodium tetraborate and ammonium pentaborate. Such electrolytes typically have an electrical conductivity of about 0.1 to about 20 mS / cm, in some embodiments about 0.5 to about 10 mS / cm, and in some embodiments about 1 to about 5 mS / cm, determined at a temperature of 25° C.If desired, each stage of anodization may be repeated through one or more cycles to achieve the desired thickness of the dielectric. Furthermore, after the first and / or second stages, the anode may also be rinsed or washed with another solvent (e.g., water) to remove the electrolyte.Solid ElectrolyteA solid electrolyte covers the dielectric, which generally acts as a cathode for the capacitor. The solid electrolyte contains a conductive polymer that is typically π-conjugated and, upon oxidation or reduction, has an electrical conductivity, such as an electrical conductivity of at least about 1 μS / cm. Examples of such π-conjugated conductive polymers are, for example, polyheterocycles (e.g., polypyrroles, polythiophenes, polyanilines, etc.), polyacetylenes, poly-p-phenylenes, polyphenolates, etc. In one embodiment, the polymer is, for example, a substituted polythiophene such as those having the following general structure: whereinT = O 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 is a linear or branched optionally substituted C 1 to C 18- alkyl radical (e.g., methyl, ethyl, n-propyl or isopropyl, n-, iso-, sec- or 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, etc.); an optionally substituted C 5- to C 12- cycloalkyl radical (e.g., cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, cyclodecyl, etc.); an optionally substituted C 6- to C 14- aryl radical (e.g., phenyl, naphthyl, etc.); an optionally substituted C 7- to C 18- aralkyl radical (e.g., benzyl, o-, m-, p-tolyl, 2,3-, 2,4-, 2,5-, 2,6-, 3,4-, 3,5-xylyl, mesityl, etc.); an optionally substituted C 1- to C 4- hydroxyalkyl radical or a hydroxy radical; andq is an integer from 0 to 8, in some embodiments 0 to 2, and in one embodiment 0; andn=2 to 5000, 4 to 2000 in some embodiments, and 5 to 1000 in some embodiments. Examples of substituents for the radicals "D" or "R 7" are, for example, alkyl, cycloalkyl, aryl, aralkyl, alkoxy, halogen, ether, thioether, disulfide, sulfoxide, sulfone, sulfonate, amino, aldehyde, keto, carboxylic acid ester, carboxylic acid, carbonate, carboxylate, cyano, alkylsilane and alkoxysilane groups, carboxylamide groups, etc.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 optionally substituted poly(3,4-ethylenedioxythiophene) having the following general structure: Methods for forming conductive polymers such as those described above are well known in the art. For example, U.S. Patent No. 6,987,663 B2 (Flager et al.), which is expressly incorporated herein by reference for all purposes, describes various techniques for forming substituted polythiophenes from a monomeric precursor. The monomeric precursor may have, for example, the following structure: wherein T, D, R, 7 and q are as defined above. Particularly suitable thiophene monomers are those in which "D" is an optionally substituted C 2- to C 3- alkylene radical. For example, optionally substituted 3,4-alkylenedioxythiophenes having the following general structure can be used: wherein R 7 and q are as defined above. In a particular embodiment, "q" = 0. A commercially suitable example of 3,4-ethylenedioxythiophene is available from H. C. Starck GmbH under the designation Clevios™ M. Other suitable monomers are also described in U.S. Patent Nos. 5,111,327 A (Blohm et al.) and 6,635,729 B1 (Groenendahl et al.), which are hereby expressly incorporated by reference for all purposes. Derivatives of these monomers, which are, for example, dimers or trimers of the above monomers, may also be used. Higher molecular weight derivatives, i.e., tetramers, pentamers, etc., of the monomers are suitable for use in the present invention. The derivatives may consist of the same or different monomer units and may be used in pure form or in a mixture with each other and / or with the monomers. Oxidized or reduced forms of these precursors may also be employed.Regardless of the particular type of polymer, the solid electrolyte comprises a layer comprising a plurality of prepolymerized particles applied in the form of a dispersion. An advantage of using a dispersion is that it can minimize the presence of ionic species (e.g. Fe 2+ or Fe 3+), which are formed during in situpolymerization, which under high electric field strength can cause dielectric breakdown due to ion migration. Thus, by applying the conductive polymer as a dispersion and not forming it by in situ polymerization, the resulting capacitor may have a relatively high "breakdown voltage.". To allow good impregnation of the anode, the particles used in the dispersion typically have a small size, such as an average size (e.g., diameter) of about 1 to about 150 nanometers, in some embodiments about 2 to about 50 nanometers, and in some embodiments about 5 to about 40 nanometers. The diameter of the particles can be determined by known techniques such as ultracentrifuge, laser diffraction, etc. The shape of the particles may also vary. In a particular embodiment, the particles are, for example, spherical. However, it should be understood that other shapes, such as plates, rods, disks, rods, tubes, irregular shapes, etc., are also contemplated by the invention. The concentration of the particles in the dispersion may vary depending upon the desired viscosity of the dispersion and the particular manner in which the dispersion is to be applied to the condenser. Typically, however, the particles comprise from about 0.1 to about 10 wt%, in some embodiments from about 0.4 to about 5 wt%, and in some embodiments from about 0.5 to about 4 wt% of the dispersion.The dispersion also generally contains a counterion which enhances the stability of the particles. That is, the conductive polymer (e.g., polythiophene or a derivative thereof) typically has a charge on the main polymer chain that is neutral or positive (cationic). Polythiophene derivatives typically carry a positive charge in the main polymer chain, for example. In some cases, the polymer may have positive and negative charges in the moiety, the positive charge being on the backbone 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 wholly saturated with the anionic groups at the radicals "R", which may be present. Overall, the polythiophenes can be cationic, neutral or even anionic in these cases. Nevertheless, they are all considered cationic polythiophenes because the polythiophene main chain carries a positive charge.The counterion can be a monomeric or polymeric anion that acts to oppose the charge of the conductive polymer. Polymeric anions may be, for example, anions of polymeric carboxylic acids (e.g., polyacrylic acids, polymethacrylic acid, polymaleic acids, etc.), polymeric sulfonic acids (e.g., polystyrene sulfonic acids ("PSS"), polyvinyl sulfonic acids, etc.), etc. The acids may also be copolymers such as copolymers of vinylcarboxylic and vinylsulfonic acids with other polymerizable monomers such as acrylic esters and styrene. Likewise, suitable monomeric anions are, 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 with C 1- to C 20- alkyl groups (e.g. benzenesulfonic acid, o-toluenesulfonic acid, p-toluenesulfonic acid or dodecylbenzenesulfonic acid); Cycloalkane sulfonic acids (e.g., camphor sulfonic acid or tetrafluoroborates, hexafluorophosphates, perchlorates, hexafluoroantimonates, hexafluoroarsenates or hexachloroantimonates); etc. Particularly suitable counterions are polymeric anions, such as a polymeric carboxylic or sulfonic acid (e.g., polystyrene sulfonic acid ("PSS")). The molecular weight of such polymeric anions is typically in the range of about 1000 to about 2,000,000, and in some embodiments about 2000 to about 500,000.When employed, the weight ratio of such counterions to conductive polymers in the dispersion and in a given layer of solid electrolyte is typically about 0.5:1 to about 50:1, in some embodiments about 1:1 to about 30:1, and in some embodiments about 2:1 to about 20:1.In addition to conductive polymers and counterions, the dispersion may also contain one or more binders to further enhance the adhesive nature of the polymeric layer and also to increase the stability of the particles within the dispersion. The binders can be organic in nature, such as polyvinyl alcohols, polyvinyl pyrrolidones, polyvinyl chlorides, polyvinyl acetates, polyvinyl butyrates, polyacrylic esters, polyacrylic amides, polymethacrylic esters, polymethacrylic amides, polyacrylonitriles, styrene / acrylic esters, vinyl acetate / acrylic 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 adhesion of the binders. Such crosslinking agents are, for example, melamine compounds, masked isocyanates or functional silanes, such as 3-glycidoxypropyl trialkoxysilane, tetraethoxysilane and tetraethoxysilane hydrolyzate, or crosslinkable polymers, such as polyurethanes, polyacrylates or polyolefins, and subsequent crosslinking.Dispersants may also be used to facilitate the formation of the solid electrolyte and the ability to apply it to the anode member. Suitable dispersing agents include solvents such as aliphatic alcohols (e.g., methanol, ethanol, i-propanol and butanol), aliphatic ketones (e.g., acetone and methyl ethyl ketone), aliphatic carboxylic 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, dimethyl acetamide and dimethyl formamide), aliphatic and araliphatic ethers (e.g., diethyl ether and anisole), Water and mixtures of any of the above solvents. A particularly suitable dispersant is water.In addition to the above, other ingredients may be used in the dispersion. For example, conventional fillers having a size of about 10 nanometers to about 100 micrometers, in some embodiments about 50 nanometers to about 50 micrometers, and in some embodiments about 100 nanometers to about 30 micrometers may be used. Examples of such fillers are calcium carbonate, silicates, silica, calcium or barium sulfate, aluminum hydroxide, glass fibers or pistons, wood flour, cellulose powder, carbon black, electrically conductive polymers etc. The fillers can be introduced into the dispersion in powder form, but can also be present in another form, for example as fibers.It is also possible to use surface-active substances in the dispersion, such as ionic or nonionic surfactants. It is also possible to use adhesives, such as organofunctional silanes or their hydrolysates, for example 3-glycidoxypropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, vinyltrimethoxysilane or octyltriethoxysilane. The dispersion may also contain additives which increase conductivity, such as ether group-containing compounds (e.g. tetrahydrofuran), lactone group-containing compounds (e.g. γ-butyrolactone or γ-valerolactone), amide or lactam group-containing compounds (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).The polymeric dispersion can be applied by a variety of known techniques, such as spin coating, impregnation, casting, drop-wise application, spraying, spraying, knife coating, brushing or printing (e.g., ink jet, screen or block printing), or dipping. Although it may vary depending on the application technique employed, the viscosity of the dispersion is typically about 0.1 to about 100000 mPa·s (measured at a shear rate of 100 s -1), in some embodiments about 1 to about 10000 mPa·s, in some embodiments about 10 to about 1500 mPa·s, and in some embodiments about 100 to about 1000 mPa·s. Once applied, the layer may be dried and washed. One or more additional layers may also be formed in this manner to achieve the desired thickness. Typically, the total thickness of the layers formed by this particle dispersion is about 1 to about 50 μm, and in some embodiments about 5 to about 20 μm. The weight ratio of counterions to conductive polymers is also about 0.5:1 to about 50:1, in some embodiments about 1:1 to about 30:1, and in some embodiments about 2:1 to about 20:1.In addition to the layer having a plurality of prepolymerized particles, the solid electrolyte further comprises a layer of hydroxyfunctional nonionic copolymer substantially free of conductive polymer.The term "hydroxy-functional" generally means that the compound contains at least one hydroxy-functional group or may have such a functional group in the presence of a solvent. Without wishing to be bound by any particular theory, we believe that hydroxy-functional nonionic polymers can improve the degree of contact between the polymer particles and the surface of the internal dielectric, which is typically relatively smooth due to higher forming stresses. This unexpectedly increases the capacitance of the resulting capacitor at low temperatures. Furthermore, we believe that the use of a hydroxy functional polymer having a particular molecular weight may also minimize the likelihood of chemical degradation. For example, the molecular weight of the hydroxy-functional polymer may be about 100 to 10000 grams per mole, in some embodiments about 200 to 2000, in some embodiments about 300 to about 1200, and in some embodiments about 400 to about 800.A large number of hydroxy-functional nonionic copolymers can generally be used for this purpose. In one embodiment, the hydroxy-functional copolymer is, for example, a polyalkylene ether. Polyalkylene ethers may include polyalkylene glycols (e.g., polyethylene glycols, polypropylene glycols, polytetramethylene glycols, polyepichlorohydrins, etc.), polyoxetanes, polyphenylene ethers, polyether ketones, etc. Polyalkylene ethers are typically predominantly linear, nonionic polymers with terminal hydroxy groups. Polyethylene glycols, polypropylene glycols and polytetramethylene glycols (polytetrahydrofurans), which are prepared by polyaddition of ethylene oxide, propylene oxide or tetrahydrofuran to water, are particularly suitable. The polyalkylene ethers can be prepared from diols or polyols by polycondensation reactions. The diol component may be selected in particular from saturated or unsaturated, branched or unbranched, aliphatic dihydroxy compounds containing 5 to 36 carbon atoms, or aromatic dihydroxy compounds, such as pentane-1,5-diol, hexane-1,6-diol, neopentyl glycol, bis(hydroxymethyl)cyclohexanes, bisphenol A, dimer diols, hydrogenated dimer diols, or else mixtures of the said diols. In addition, polyhydric alcohols including, for example, glycerol, di- and polyglycerol, trimethylolpropane, pentaerythritol or sorbitol may also be used in the polymerization reaction.In addition to those mentioned above, other hydroxy-functional nonionic polymers can also be used in the present invention. Some examples of such polymers are, for example, ethoxylated alkyl phenols, ethoxylated or propoxylated C 6- C 24- fatty alcohols, polyoxyethylene glycol alkyl ethers having the general formula CH 3-( CH 2)10-16-( O-C 2 H 4)1-25- OH (e.g. octaethylene glycol monododecyl ether and pentaethylene glycol monododecyl ether); polyoxypropylene glycol alkyl ethers having the general formula CH 3-( CH 2)10-16-( O-C 3 H 6)1-25- OH; A polyoxyethylene glycol octylphenol ether having the following general formula: C 8 H 17-( C 6 H 4)-( O-C 2 H 4)1-25- OH (e.g., TritonNH X-100); polyoxyethylene glycol alkylphenol ether having the following general formula: C 9 H 19-( C 6 H 4)-( O-C2H4)NER80_-OH (e.g., nonoxynol-9); Polyoxyethylene glycol esters of C 8- C 24- fatty acids such as polyoxyethylene glycol sorbitan alkyl ester (e.g., Polyoxyethylen(20)sorbitanmonolaurat Polyoxyethylen(20)sorbitanmonopalmitat polyoxyethylene (20) sorbitan monostearate, Polyoxyethylen(20)sorbitanmonooleat PEG-20 methyl glucose distearate, PEG-20 methyl glucose sesquistearate, PEG-80 castor oil and PEG-20 castor oil, PEG-3 castor oil, PEG-600 dioleate and PEG-400 dioleate) and polyoxyethylene glycerol alkyl ester (e.g., polyoxyethylene-23 glycerol laurate and polyoxyethylene-20 glycerol stearate); Polyoxyethylene glycol ethers of C 8- C 24- fatty acids (e.g., polyoxyethylene 10-cetyl ether, polyoxyethylene 10-stearyl ether, polyoxyethylene 20-cetyl ether, polyoxyethylene 10-oleyl ether, polyoxyethylene 20-oleyl ether, polyoxyethylene 20-isohexadecyl ether, polyoxyethylene 15-tridecyl ether and polyoxyethylene 6-tridecyl ether); block copolymers of polyethylene glycol and polypropylene glycol (e.g., poloxamers), etc., and mixtures thereof.The hydroxyfunctional nonionic copolymer can be incorporated into the solid electrolyte in a variety of different ways. For example, in certain embodiments, the hydroxy-functional copolymer can be readily incorporated into any layers formed by the preliminary dispersion described above. In such embodiments, the concentration of the hydroxy functional polymer in the dispersion is typically about 1 wt% to about 50 wt%, in some embodiments about 5 wt% to about 40 wt%, and in some embodiments about 10 wt% to about 30 wt%.However, in other embodiments, the hydroxy-functional polymer may be applied after the first polymer dispersion is applied to the anode body. In such embodiments, the technique used to apply the hydroxy-functional polymer may vary. For example, the polymer may be applied in the form of a liquid solution by various methods such as dipping, dipping, pouring, dripping, spraying, spreading, brushing or printing, for example by ink jet, screen printing or pad printing. Solvents known to the skilled person, such as water, alcohols or a mixture thereof, can be used in the solution. The concentration of the hydroxy functional polymer in such a solution is typically in the range of about 5% to about 95%, in some embodiments about 10% to about 70%, and in some embodiments about 15% to about 50%, by weight of the solution. According to the invention, such solutions are substantially free of conductive polymers. That is, in accordance with the invention, conductive polymers comprise about 2% or less by weight, in some embodiments about 1% or less by weight, and in some embodiments about 0.5% or less by weight of the solution.Alternatively, however, it may also be desirable to employ a conductive polymer in combination with the hydroxy-functional polymer. For example, in certain embodiments, a second polymer dispersion containing conductive polymer particles and a hydroxy-functional polymer is applied to the anode after the first layers formed from the first polymer dispersion are applied to the anode body. The conductive particles of the second polymer dispersion are generally described above, although they need not be identical to those used in the first polymer dispersion. For example, particles of different size and / or chemical composition may be used in the first and second polymer dispersions. Regardless, the concentration of the hydroxy-functional polymer in the second polymer dispersion is typically about 1 wt % to about 50 wt %, in some embodiments about 5 wt % to about 40 wt %, and in some embodiments about 10 wt % to about 30 wt %. Likewise, in those embodiments where the hydroxy-functional polymer is employed in a second dispersion, it may also be desirable that the first dispersion be substantially free of such hydroxy-functional nonionic polymers. For example, hydroxy-functional polymers may constitute about 2 wt % or less, in some embodiments about 1 wt % or less, and in some embodiments about 0.5 wt % or less of the first polymer dispersion. Once applied, the layer formed by the second polymer dispersion may be dried and / or washed. One or more additional layers may also be formed in this manner to achieve the desired thickness. Typically, the total thickness of the layers formed by the second polymer dispersion is about 0.1 to about 5 μm, in some embodiments about 0.1 to about 3 μm, and in some embodiments about 0.2 to about 1 μm.External Polymer CoatingAlthough not required, an external polymer coating may also be applied to the anode body and cover the solid electrolyte. The external polymer coating generally contains one or more layers formed from a dispersion of prepolymerized conductive particles as described in more detail above. The external coating may be able to penetrate further into the edge region of the capacitor body to increase adhesion to the dielectric and result in a more mechanically robust part that may reduce equivalent series resistance and leakage current. Since one generally wants to improve the degree of edge coverage and not impregnate the interior of the anode, the particles used in the external coating are typically larger than those used in any optional solid electrolyte dispersions. For example, the ratio of the average size of the particles used in the external polymer coating to the average size of the particles used in any solid electrolyte dispersion is typically about 1.5 to about 30, in some embodiments about 2 to about 20, and in some embodiments about 5 to about 15.If desired, a crosslinking agent may also be used in the external polymer coating to increase the degree of adhesion to the solid electrolyte. Typically, the crosslinking agent is applied prior to application of the dispersion used in the external coating. Suitable crosslinking agents are described, for example, in U.S. Patent Publication US 2007 / 0 064 376 A1 (Flager et al.) and include, for example, amines (e.g., diamines, triamines, oligomer amines, polyamines, etc.); Polyvalent metal cations such as salts or compounds of Mg, Al, Ca, Fe, Cr, Mn, Ba, Ti, Co, Ni, Cu, Ru, Ce or Zn, phosphonium compounds, sulfonium compounds, etc. Particularly suitable examples are, for example, 1,4-diaminocyclohexane, 1,4-bis(aminomethyl)cyclohexane, ethylenediamine, 1,6-hexanediamine, 1,7-heptanediamine, 1,8-octanediamine, 1,9-nonanediamine, 1,10-decanediamine, 1,12-dodecanediamine, N,N-dimethylethylenediamine, N,N,N',N'-tetramethylethylenediamine, N,N,N',N'-tetramethyl-1,4-butanediamine, etc., and mixtures thereof.The crosslinking agent is typically applied from a solution or dispersion whose pH is from 1 to 10, in some embodiments from 2 to 7, and in some embodiments from 3 to 6, determined at 25°C. Acidic compounds can be used to assist in achieving the desired pH. Examples of solvents or dispersing agents for the crosslinking agent are water or organic solvents such as alcohols, ketones, carboxylic esters, etc. The crosslinking agent can be applied to the capacitor body by any known method such as spin coating, impregnation, casting, drop-wise application, spray application, evaporation, sputtering, sublimation, blade coating, painting or printing, for example, by ink jet, screen printing or pad printing. Once applied, the crosslinking agent can be dried before the polymer dispersion is applied. This process can then be repeated until the desired thickness is reached. For example, the total thickness of the entire external polymer coating including the crosslinking agent and the dispersion layers may be in the range of about 1 to about 50 μm, in some embodiments about 2 to about 40 μm, and in some embodiments about 5 to about 20 μm.V. Other Components of CapacitorIf desired, the capacitor may also include other layers as is known in the art. For example, a protective coating may optionally be formed between the dielectric and the solid electrolyte, such as a relatively insulating resinous material (natural or synthetic). Such materials may have a resistivity of greater than about 10 Ω·cm, in some embodiments greater than about 100, in some embodiments greater than about 1000 Ω·cm, in some embodiments greater than about 1×10 5 Ω·cm, and in some embodiments greater than about 1×10 10 Ω·cm. Some resinous materials which may be used in the present invention include, but are not limited to, polyurethane, polystyrene, esters of unsaturated or saturated fatty acids (e.g., glycerides), etc. Suitable esters of fatty acids include, for example, 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, schellic acid, etc. These esters of fatty acids have been found to be particularly useful when used in relatively complex combinations to form a "drying oil" which allows the resulting film to rapidly polymerize to a stable layer. Such drying oils include, for example, mono-, di- and / or triglycerides having a glycerol backbone with one, two or three fatty acyl residues esterified. Some suitable drying oils that may be used include 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 (Fife et al.), which is expressly incorporated herein by reference for all purposes.If desired, a carbon layer (e.g., graphite) or a silver layer may also be applied to the part. The silver coating may act as, for example, a solderable conductor, contact layer and / or charge collector for the capacitor, and the carbon coating may restrict contact of the silver coating with the solid electrolyte. Such coatings may cover a portion or all of the solid electrolyte.The capacitor may also be provided with end portions, particularly when used in surface mount applications. For example, the capacitor may include an anode end portion to which the anode lead wire of the capacitor element is electrically connected and a cathode end portion to which the cathode of the capacitor element is electrically connected. Any conductive material may be used to form the end portions, such as a conductive metal (e.g., copper, nickel, silver, zinc, tin, palladium, lead, copper, aluminum, molybdenum, titanium, iron, zirconium, magnesium, and alloys thereof). Particularly suitable conductive metals include, for example, 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 end portions is generally selected to minimize the thickness of the capacitor. For example, the thickness of the end portions may range from about 0.05 to about 1 millimeter, in some embodiments from about 0.05 to about 0.5 millimeter, or from about 0.07 to about 0.2 millimeter. An exemplary conductive material is a metal plate of a copper-iron alloy available from Wieland (Germany). If desired, the surface of the end portions may be electroplated with nickel, silver, gold, tin, etc. as is known in the art to ensure that the final portion is mountable on the circuit board. In a particular embodiment, both surfaces of the end parts are provided with nickel and silver protective layers respectively, while the mounting surface is also provided with a tin soldering layer.FIG. 1 shows an embodiment of an electrolytic capacitor 30 that includes an anode end portion 62 and a cathode end portion 72 in electrical communication with a capacitor element 33. The capacitor element 33 has an upper surface 37, a lower surface 39, a front surface 36, and a rear surface 38. Although the cathode end portion 72 may be in electrical contact with any surface of the capacitor element 33, in the embodiment shown it is in electrical contact with the bottom surface 39 and the back surface 38. 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.The anode end portion 62 also includes a first component 63 positioned substantially perpendicular to a second component 64. The first component 63 is in electrical contact and substantially parallel with the bottom surface 39 of the capacitor element 33. the second component 64 includes a region 51 that supports an anode lead 16. In the embodiment shown, the region 51 has a "U-shape" to further increase the surface contact and mechanical stability of the lead 16.The end portions may be connected to the capacitor element using any method known in the art. For example, in one embodiment, a lead frame may be provided that defines the cathode end portion 72 and the anode end portion 62. To attach the electrolytic capacitor element 33 to the lead frame, a conductive adhesive may be first applied to a surface of the cathode end portion 72. The conductive adhesive may include, for example, conductive metal particles contained in a resin composition. The metal particles may be silver, copper, gold, platinum, nickel, zinc, bismuth, etc. The resin composition may include a thermosetting resin (e.g., epoxy resin), curing agent (e.g., acid anhydride), and coupling agent (e.g., silane coupling agent). Suitable conductive adhesives are described in U.S. patent application US 2006 / 0 038 304 A1 (Osako et al.), which is expressly incorporated herein by reference for all purposes. A variety of techniques may be used to apply the conductive adhesive to the cathode end portion 72. For example, printing techniques may be employed due to their practical and cost-effective utility.In general, a variety of methods may be employed to attach the end portions to the capacitor. For example, in one embodiment, the second component 64 of the anode end portion 62 and the second component 74 of the cathode end portion 72 are first bent upwardly to the position shown in FIG. 1. Thereafter, the capacitor element 33 is positioned on the cathode end portion 72 so that its lower surface 39 comes into contact with the adhesive and the anode lead wire 16 is received by the upper U-shaped portion 51. If desired, an insulating material (not shown), such as a plastic pad or tape, may be located between the bottom surface 39 of the capacitor element 33 and the first component 63 of the anode end portion 62 to electrically isolate the anode and cathode end portions from each other.Then, the anode terminal 16 is electrically connected to the region 51 by a method known in the art, such as mechanical welding, laser welding, conductive adhesives, etc. For example, the anode terminal 16 may be welded to the anode end portion 62 by a laser.Lasers generally include resonators that contain a lasing medium capable of releasing photons by stimulated emission and a power source that excites the elements of the lasing medium. One type of suitable laser is one in which the laser medium is an aluminum yttrium garnet (YAG) doped with neodymium (Nd). The excited particles are neodymium ions Nd 3+. The energy source may provide continuous energy to the laser medium to emit a continuous laser beam or energy discharges to emit a pulsed laser beam. After electrically connecting the anode terminal 16 to the anode end portion 62, the conductive adhesive may then be cured. For example, a heating press may be used to apply heat and pressure to ensure that the electrolytic capacitor element 33 is sufficiently strongly adhered to the cathode end portion 72 by the adhesive.Once the capacitor element is attached, the leadframe may be enclosed in a resin package, which may then be filled with silicon oxide or any other known embedding material. The width and length of the housing may vary depending on the intended use. Suitable housings include, for example, housings "A", "B", "C", "D", "E", "F", "G", "H", "J", "K", "L", "M", "N", "P", "R", "S", "T", "V", "W", "Y", "X", or "Z" (AVX Corporation). Regardless of the package size employed, the capacitor element is embedded such that at least a portion of the anode and cathode end portions remain exposed for mounting on a printed circuit board. For example, as shown in FIG. 1, the capacitor element 33 is embedded in a case 28 such that a part of the anode end part 62 and a part of the cathode end part 72 are exposed.As a result of the present invention, the capacitor assembly can have excellent electrical characteristics as mentioned above. For example, the capacitor may have a relatively high capacitance. The dry capacitance may be relatively similar to the wet capacitance, enabling the capacitor to have little capacitance loss and / or fluctuation in the presence of humidity. This performance characteristic is quantified by the "wet-to-dry percent capacity" determined by the equation.The capacitor of the present invention may have, for example, a wet-to-dry percentage capacitance of about 50% or more, in some embodiments about 60% or more, in some embodiments about 70% or more, and in some embodiments about 80% to 100%. In addition to stable capacitance, the capacitor may also maintain a low equivalent series resistance ("ESR") under the above conditions, such as less than about 100 milliohms, in some embodiments less than about 75 milliohms, in some embodiments about 0.01 to about 60 milliohms, and in some embodiments about 0.05 to about 50 milliohms, as measured at an operating frequency of 100 kHz. In certain cases, this improved capacity and ESR properties may remain stable under a variety of different conditions. For example, the capacitance and / or equivalent series resistance of the capacitor may be within the above ranges even at low or low temperatures, such as about 25° C. or less, about 10° C. or less in some embodiments, about 0° C. or less in some embodiments, and about -75° C. to about -25° C. (e.g., -55° C.), as well as over wide frequency ranges, such as about 10 Hz to about 100 kHz in some embodiments.The leakage current, which generally refers to the current flowing from one conductor through an insulator to an adjacent conductor, can also be maintained at relatively low levels. For example, the numerical value of the normalized leakage current of a capacitor of the present invention is less than about 1 μA / μF·V in some embodiments, less than about 0.5 μA / μF·V in some embodiments, and less than about 0.1 μA / μF·V in some embodiments, where "μA" means microampere and "μF·V" is the product of the capacitance and the rated voltage. These normalized leakage current values can be maintained even after aging, which occurs at high temperatures for a significant period of time. For example, the values may be maintained for about 100 hours or longer, in some embodiments from about 300 hours to about 3000 hours, and in some embodiments from about 400 hours to 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 -55° C. to about 250° C., in some embodiments from about 0° C. to about 225° C., and in some embodiments from about 10° C. to about 225° C.The present invention will be more fully understood from the following examples.Test MethodsEquivalent Series Resistance (ESR)The equivalent series resistance can be measured using a Keithley 3330 Precision LCZ meter with Kelvin connections, 2.2 volts bias, and a 0.5 volt peak-to-peak sinusoidal signal. The operating frequency was 100 kHz and the temperature was room temperature.Dry and Wet CapacityCapacitance was measured using a Keithley 3330 Precision LCZ meter with Kelvin connections, 2.2 volts bias, and a 0.5 volt peak-to-peak sinusoidal signal. The operating frequency was 120 Hz and the temperature was room temperature. The "dry capacitance" refers to the capacitance of the device after deposition of the solid electrolyte, graphite and silver layers, while the "wet capacitance" refers to the capacitance of the device after formation of the dielectric, as measured in 17% sulfuric acid and based on a 1 mF tantalum cathode.Example 1A tantalum powder at 8500 μFV / g was used to form anode samples. Each anode sample was embedded together with a tantalum wire, sintered at 180° C. and pressed to a density of 5.6 g / cm 3. The resulting compacts were 5.20 mm x 3.70 mm x 0.85 mm in size. The pellets were anodized at a temperature of 85° C. in water / phosphoric acid electrolyte having a conductivity of 8.6 mS to 72.5 V to form the dielectric layer. The pellets were re-anodized for 30 seconds at a temperature of 30°C in water / boric acid / disodium tetraborate having a conductivity of 2.0 mS up to 160 V to form a thicker oxide layer that builds up on the outside. A conductive polymer coating was then formed by immersing the anodes in dispersed poly(3,4-ethylenedioxythiophene) having a solids content of 1.1% and a viscosity of 20 mPa·s (Clevios™ K, H.C. Starck). After coating, the parts were dried at 125°C for 20 minutes. This procedure was repeated ten times. Thereafter, the parts were immersed in dispersed poly(3,4-ethylenedioxythiophene) having a solid content of 2% and a viscosity of 20 mPa·s (Clevios™ K, H.C. Starck). After coating, the parts were dried at 125°C for 20 minutes. This procedure was not repeated. Thereafter, the parts were immersed in dispersed poly(3,4-ethylenedioxythiophene) having a solid content of 2% and a viscosity of 160 mPa·s (Clevios™ K, H.C. Starck). After coating, the parts were dried at 125°C for 20 minutes. This procedure was repeated eight times. Then, the parts were immersed in a graphite dispersion and dried. Finally, the parts were immersed in a silver dispersion and dried. Many 22 μF / 25 V capacitor parts (200) were fabricated in this manner.Example 2A tantalum powder at 34000 μFV / g was used to form anode samples. Each anode sample was embedded together with a tantalum wire, sintered at 1440 °C, and pressed to a density of 5.8 g / cm 3. The resulting compacts were 5.20 mm x 3.70 mm x 0.85 mm in size. The pellets were anodized at a temperature of 85° C. in water / phosphoric acid electrolyte having a conductivity of 8.6 mS to 96.0 V to form the dielectric layer. The pellets were re-anodized to 130 V for 30 seconds (2 cycles) at a temperature of 30° C. in water / boric acid / disodium tetraborate having a conductivity of 2.0 mS to form a thicker oxide layer that builds up on the outside. Then, a conductive polymer coating, a graphite coating and a silver coating were formed in the same manner as described in Example 1. Many 33 μF / 25 V capacitor parts (200) were fabricated in this manner.Example 3Capacitors were formed in the manner described in Example 2 except that a different conductive polymer coating was used. A conductive polymer coating was formed by immersing the anodes in a dispersion of poly(3,4-ethylenedioxythiophene) having a solids content of 1.1% and a viscosity of 20 mPa·s (Clevios™ K, H.C. Starck). After coating, the parts were dried at 125 °C for 20 minutes. This procedure was repeated ten times. Thereafter, the parts were immersed in a dispersion of poly(3,4-ethylenedioxythiophene) having a solids content of 2% and a viscosity of 20 mPa·s (Clevios™ K, H.C. Starck) and an additional solids content of 20% of polyethylene glycol having a molecular weight of 600 (Sigma Aldrich ®). After coating, the parts were dried at 125°C for 20 minutes. This procedure was not repeated. Thereafter, the parts were immersed in a dispersion of poly(3,4-ethylenedioxythiophene) having a solids content of 2% and a viscosity of 160 mPa s (Clevios™ K, H.C. Starck). After coating, the parts were dried at 125°C for 20 minutes. This procedure was repeated eight times. Then, the parts were immersed in a graphite dispersion and dried. Finally, the parts were immersed in a silver dispersion and dried. Many 33 μF / 25 V capacitor parts (200) were fabricated in this manner.Then, the finished capacitors of Examples 1-3 were tested for electrical properties prior to an assembly process. The medians of the results on capacity, Df and ESR are shown below in Table 1. The wet capacity was 25.1 μF for Example 1 and 38.0 μF for Example 2-3. Table 1. electrical properties Table 1. electrical propertiesExample 121,083,75,0544,3Example 232,485,44,4035,1Example 334,590,74,6436,4As indicated, the polyethylene glycol portions (Example 3) achieved a higher capacity than those of Examples 1 and 2.

Claims

A solid electrolytic capacitor comprising: a sintered porous anode formed from a finely divided powder having a specific charge of greater than about 30,000 μF*V / g, the powder containing particles having a three-dimensional shape; a dielectric layer covering the anode body; and a solid electrolyte covering the dielectric layer, the solid electrolyte comprising a layer comprising a plurality of prepolymerized conductive polymer particles and further comprising a layer of hydroxyfunctional nonionic copolymer substantially free of conductive polymer; wherein the capacitor has a breakdown voltage of about 60 V or more.The solid electrolytic capacitor according to claim 1, wherein the particles are spheroidal.The solid electrolytic capacitor according to claim 1 or 2, wherein the powder has a specific charge of about 35000 to about 45000 μF*V / g.The solid electrolytic capacitor of any preceding claim, wherein the anode contains from about 2500 to about 6000 ppm oxygen.The solid electrolytic capacitor according to any preceding claim, wherein the prepolymerized particles are formed from a substituted polythiophene such as poly(3,4-ethylenedioxythiophene).The solid electrolytic capacitor according to claim 4, wherein the prepolymerized particles contain a monomeric or polymeric counter anion such as polystyrene sulfonic acid.The solid electrolytic capacitor of any preceding claim, wherein the prepolymerized particles have an average size of about 2 to about 50 nanometers.The solid electrolytic capacitor according to claim 1, wherein the hydroxy-functional nonionic copolymer is a polyalkylene ether such as a polyalkylene glycol.The solid electrolytic capacitor of any preceding claim, further comprising an external polymer coating covering the solid electrolyte, wherein the external polymer coating contains a plurality of prepolymerized conductive polymer particles, and wherein the prepolymerized particles of the external polymer coating have a larger average size than the prepolymerized particles of the solid electrolyte.The solid electrolytic capacitor of any preceding claim, wherein the capacitor has a breakdown voltage of about 80 volts or more and / or a wet-to-dry capacitance of about 50% or more.A method of forming the solid electrolytic capacitor of any preceding claim, the method comprising: pressing a particulate powder in the form of a pellet, the powder having a specific charge greater than about 30000 μF*V / g and containing particles having a three-dimensional shape; sintering the pellet; anodizing the sintered pellet to form a dielectric layer covering the anode; and applying a dispersion of prepolymerized conductive polymer particles to the dielectric layer and further applying a hydroxy-functional non-ionic copolymer substantially free of conductive polymer.The method of claim 11, wherein the compact is sintered at a temperature of about 1350°C to about 1600°C.The method of claim 11, wherein the press density is about 5.0 to about 6.5.

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