Electrolytic capacitors with polymeric outer layer

The invention relates to electrolytic capacitors with a low equivalent series resistance and low residual current consisting of a solid electrolyte made of conductive polymers and an outer layer containing conductive polymers and polymeric anions, their production and the use of such electrolytic capacitors.

A solid electrolyte capacitor usually consists of a porous metal electrode, an oxide layer on the metal surface, an electrically conductive solid that is introduced into the porous structure, an outer electrode, such as a silver layer, as well as further electrical contacts and an encapsulation.

Examples of solid electrolyte capacitors are tantalum, aluminum, niobium and niobium oxide capacitors with charge transfer complexes, brown stone or polymer solid electrolytes. The use of porous bodies has the advantage that, due to the large surface area, very high capacitance densities, ie high electrical capacities in a small space, can be achieved.

Due to their high electrical conductivity, π-conjugated polymers are particularly suitable as solid electrolytes. π-conjugated polymers are also referred to as conductive polymers or as synthetic metals. They are becoming increasingly important economically, since polymers have advantages over metals in terms of processability, weight and the targeted adjustment of properties through chemical modification. Examples of known π-conjugated polymers are polypyrroles, polythiophenes, polyanilines, polyacetylenes, polyphenylenes and poly (p-phenylene-vinylenes), a particularly important and technically used polythiophene being poly-3,4- (ethylene-1,2-dioxy ) thiophene, often referred to as poly (3,4-ethylenedioxythiophene), because it has very high conductivities in its oxidized form.

The technical development in electronics increasingly requires solid electrolytic capacitors with very low equivalent series resistances (ESR). The reasons for this are, for example, falling logic voltages, a higher integration density and increasing clock frequencies in integrated circuits. A low ESR also lowers energy consumption, which is particularly advantageous for mobile, battery-operated applications. There is therefore a desire to reduce the ESR of solid electrolytic capacitors as much as possible.

In the European patent specification <patcit id="pcit0001" dnum="EP340512A"><text>EP-A 340 512</text></patcit> describes the production of a solid electrolyte from 3,4-ethylene-1,2-dioxythiophene and the use of its cationic polymer produced by oxidative polymerization as a solid electrolyte in electrolytic capacitors. Poly (3,4-ethylenedioxythiophene) as a replacement for manganese dioxide or charge transfer complexes in solid electrolytic capacitors lowers the equivalent series resistance of the capacitor due to its higher electrical conductivity and improves the frequency response.

In addition to a low ESR, modern solid electrolytic capacitors require a low residual current and good stability against external loads. Particularly during the manufacturing process, high mechanical loads occur during the encapsulation of the capacitor anodes, which can greatly increase the residual current of the capacitor anode.

Stability against such loads and thus a low residual current can be achieved above all by an approx. 5-50 µm thick outer layer made of conductive polymers on the capacitor anode. Such a layer serves as a mechanical buffer between the capacitor anode and the electrode on the cathode side. This prevents the electrode, for example in the event of mechanical stress comes into direct contact with the anode or damages it, thereby increasing the residual current of the capacitor. The conductive polymer outer layer itself has a so-called self-healing behavior: Small defects in the dielectric on the outer anode surface, which occur despite the buffer effect, are electrically isolated by the fact that the conductivity of the outer layer at the defect is destroyed by the electrical current.

The formation of a thick outer layer by means of in-situ polymerization is very difficult. The layer formation requires very many coating cycles. Due to the large number of coating cycles, the outer layer is very inhomogeneous, in particular the edges of the capacitor anode are often insufficiently covered. The<patcit id="pcit0002" dnum="JP2003188052A"><text>Japanese patent application JP-A 2003-188052</text></patcit> describes that homogeneous edge assignment requires complex coordination of the process parameters. However, this makes the manufacturing process very susceptible to interference. Adding binder materials for faster layer build-up is also difficult, since the binder materials hinder the oxidative in-situ polymerization. In addition, the in-situ polymerized layer usually has to be freed of residual salts by washing, which creates holes in the polymer layer.

A dense outer layer with good edge coverage can be achieved by electrochemical polymerization. However, electrochemical polymerization requires that a conductive film is first deposited on the insulating oxide layer of the capacitor anode and then this layer is electrically contacted for each individual capacitor. This contacting is very complex in mass production and can damage the oxide layer.

The use of formulations containing the powder of a conductive polymer and binder have too high an electrical resistance due to the high contact resistances between the individual powder particles to enable the production of solid electrolytic capacitors with low ESR.

In the <patcit id="pcit0003" dnum="JP2001102255A"><text>Japanese patent applications JP-A 2001-102255</text></patcit> and <patcit id="pcit0004" dnum="JP2001060535A"><text>JP-A 2001-060535</text></patcit> For the protection of the oxide film and the better adhesion of the solid electrolyte to the oxide film, a layer of polyethylene dioxythiophene / polystyrene sulfonic acid (PEDT / PSS), also known as polyethylene dioxythiophene / polystyrene sulfonic acid complex or PEDT / PSS complex, is applied directly to the oxide film. The outer layer is then applied to this layer by means of in-situ polymerization or by impregnating the capacitor anode with tetracyanoquinodimethane salt solution. However, this method has the disadvantage that the PEDT / PSS complex does not penetrate into porous anode bodies with small pores. As a result, modern, highly porous anode materials cannot be used.

<patcit id="pcit0005" dnum="US6001281P"><text>U.S. P 6,001,281</text></patcit> and <patcit id="pcit0006" dnum="US6056899P"><text>US-P 6,056,899</text></patcit> describe in the examples capacitors with a solid electrolyte made of in-situ produced polyethylene dioxythiophene (PEDT) and an outer layer of PEDT / PSS complex. A disadvantage of these capacitors<patcit id="pcit0007" dnum="US6001281P"><text>U.S. P 6,001,281</text></patcit> is that they have a high ESR of 130 mΩ and larger.

There is therefore still a need for solid electrolytic capacitors with a low equivalent series resistance (ESR) which have a dense polymeric outer layer with good edge coverage and a low residual current. There is also a need for a method of manufacturing such capacitors.

The task was therefore to provide such capacitors.

It has now surprisingly been found that solid electrolytic capacitors which have a solid electrolyte made of a conductive material, preferably a conductive polymer and an outer layer containing a polymeric anion, polyanilines and / or polythiophenes and a polymeric organic binder meet these requirements.

The present invention therefore relates to an electrolytic capacitor containing a porous electrode body of an electrode material a dielectric covering the surface of the electrode material, a solid electrolyte containing a conductive material, preferably a conductive polymer, which completely or partially covers the dielectric surface, a layer on all or part of the outer surface of the porous electrode body covered with a dielectric and wholly or partially with a solid electrolyte containing at least one polymeric anion and at least one optionally substituted polyaniline and / or at least one polythiophene with repeating units of the general formula (I ), (II) or recurring units of the general formulas (I) and (II),<chemistry id="chem0001" num="0001"><img file="EP1524678B2_D0001.tif" /></chemistry>wherein<dl id="dl0001"><dt>A</dt><dd>for an optionally substituted C₁-C₅-Alkylene radical stands,</dd><dt>R</dt><dd>for a linear or branched, optionally substituted C₁-C₁₈Alkyl radical, an optionally substituted C₅-C₁₂-Cycloalkylrest, an optionally substituted C₆-C₁₄Aryl radical, an optionally substituted C₇-C₁₈Aralkyl radical, an optionally substituted C₁-C₄-Hydroxyalkyl radical or a hydroxyl radical,</dd><dt>x</dt><dd>represents an integer from 0 to 8 and</dd></dl>in the event that several radicals R are bonded to A, these may be the same or different, characterized in that the layer containing at least one polymeric anion and at least one optionally substituted polyaniline and / or at least one polythiophene with repeating units of the general formula ( I), (II) or repeating units of the general formula (I) and (II) contains at least one polymeric organic binder.

The general formulas (I) and (II) are to be understood such that the substituent R can be bonded to the alkylene radical A x times.

The electrode material in the electrolytic capacitor according to the invention preferably forms a porous body with a large surface, for example in the form of a porous sintered body or a roughened film. In the following, this is also referred to as electrode body.

The electrode body covered with a dielectric is also briefly referred to below as the oxidized electrode body. The term “oxidized electrode body” also includes those electrode bodies that are covered with a dielectric that was not produced by oxidation of the electrode body.

The electrode body covered with a dielectric and wholly or partially with a solid electrolyte is also referred to below as the capacitor body.

The layer containing at least one polymeric anion and at least one optionally substituted polyaniline and / or at least one polythiophene with repeating units of the general formula (I), (II) or repeating units of the general formula (I) and (II), which are based on the outer surface, is referred to below as a polymeric outer layer.

The polymeric outer layer contains at least one polymeric, organic binder. As polymeric organic binder, for example, come polyvinyl alcohols, polyvinyl pyrrolidones, polyvinyl chlorides, polyvinyl acetates, polyvinyl butyrates, polyacrylic acid esters, Polyacrylsäureamide, polymethacrylic, Polymethacrylsäureamide, polyacrylonitriles, styrene / acrylate, vinyl acetate / acrylate and ethylene / vinyl acetate copolymers, polybutadienes, polyisoprenes, polystyrenes, polyethers , Polyester, polycarbonates, polyurethanes, polyamides, polyimides, polysulfones, Melamine-formaldehyde resins, epoxy resins, silicone resins or celluloses in question. Furthermore, in the context of the invention, polymeric organic binders are also those which, by adding crosslinkers such as, for example, melamine compounds, blocked isocyanates or functional silanes, such as, for example, 3-glycidoxypropyltrialkoxysilane, tetraethoxysilane and tetraethoxysilane hydrolyzate, or crosslinkable polymers such as, for example Polyurethanes, polyacrylates or polyolefins and subsequent crosslinking are generated. Such crosslinking products suitable as polymeric binders can also be formed, for example, by reacting the added crosslinking agents with the polymeric anions. The crosslinked polyanion in the polymeric outer layer then takes on both the function of the polymeric anion and that of the polymeric organic binder. Capacitors containing such crosslinked polyanions are also to be understood as capacitors in the context of this invention. Preferred polymeric organic binders are those which have sufficient temperature stability to withstand the temperature loads to which the finished capacitors are later exposed, for example soldering temperatures of 220 to 260 ° C.

The proportion of the polymeric binder in the outer layer is 1-90%, preferably 5-80% and very particularly preferably 20-60%.

For the purposes of the invention, the term polymers encompasses all compounds with more than one identical or different repeating unit.

Conductive polymers are understood here to mean the class of compounds of the π-conjugated polymers which have an electrical conductivity after oxidation or reduction. For the purposes of the invention, such π-conjugated polymers are preferably understood to be conductive polymers which have electrical conductivity after oxidation.

The prefix poly in the context of the invention means that more than one identical or different repeating unit is contained in the polymer or polythiophene. The polythiophenes contain a total of n recurring units of the general formula (I), (II) or of the general formulas (I) and (II), where n is an integer from 2 to 2000, preferably 2 to 100. The repeating units of the general formula (I) and / or (II) can in each case be the same or different within a polythiophene. Polythiophenes with the same recurring units of the general formula (s) (I), (II) or (I) and (II) are preferred.

The polythiophenes preferably each carry H.

The solid electrolyte can contain optionally substituted polythiophenes, polypyrroles and polyanilines as conductive polymers.

Preferred conductive polymers in the sense of the invention are polythiophenes having repeating units of the general formula (I), (II) or repeating units of the general formula (I) and (II), in which A, R and x are those described above for the general formulas (I ) and (II) have the meaning given.

Particularly preferred are polythiophenes with repeating units of the general formula (I), (II) or repeating units of the general formula (I) and (II), in which A represents an optionally substituted C₂-C₃Alkylene radical and x is 0 or 1.

Poly (3,4-ethylenedioxythiophene) is very particularly preferred as the conductive polymer of the solid electrolyte.

C.₁-C₅Alkylene radicals A are methylene, ethylene, n-propylene, n-butylene or n-pentylene in the context of the invention. C.₁-C₁₈In the context of the invention, alkyl stands for linear or branched C.₁-C₁₈Alkyl residues such as methyl, ethyl, n- 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 or n-octadecyl, C₅-C₁₂-Cycloalkyl for C₅-C₁₂-Cycloalkyl radicals such as cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl or cyclodecyl, C₅-C₁₄Aryl for C₅-C₁₄Aryl radicals such as phenyl or naphthyl, and C₇-C₁₈Aralkyl for C₇-C₁₈Aralkyl radicals such as benzyl, o-, m-, p-tolyl, 2,3-, 2,4-, 2,5-, 2,6-, 3,4-, 3,5-xylyl or mesityl. The above list serves to explain the invention by way of example and is not to be regarded as conclusive.

As further substituents of the C₁-C₅Alkylene radicals A are numerous organic groups, for example alkyl, cycloalkyl, aryl, halogen, ether, thioether, disulfide, sulfoxide, sulfone, sulfonate, amino, aldehyde, keto, Carboxylic acid ester, carboxylic acid, carbonate, carboxylate, cyano, alkylsilane and alkoxysilane groups and carboxylamide groups.

The polythiophenes contained as solid electrolytes in the electrolytic capacitors according to the invention can be neutral or cationic. In preferred embodiments, they are cationic, with "cationic" referring only to the charges that sit on the polythiophene backbone. Depending on the substituent on the radicals R, the polythiophenes can carry positive and negative charges in the structural unit, the positive charges on the polythiophene main chain and the negative charges optionally being on the radicals R substituted by sulfonate or carboxylate groups. The positive charges of the polythiophene main chain can be partially or completely saturated by the anionic groups which may be present on the radicals R. Overall, the polythiophenes in these cases can be cationic, neutral, or even anionic. Nevertheless, they are all considered cationic polythiophenes in the context of the invention, since the positive charges on the polythiophene main chain are decisive. The positive charges are not shown in the formulas because their exact number and position cannot be determined correctly. However, the number of positive charges is at least 1 and at most n, where n is the total number of all recurring units (identical or different) within the polythiophene.

The cationic polythiophenes require anions as counterions to compensate for the positive charge, provided that this is not already done by the optionally substituted sulfonate or carboxylate and thus negatively charged radicals R.

Counterions can be monomeric or polymeric anions, the latter also referred to below as polyanions.

Polymeric anions can, for example, anions of polymeric carboxylic acids, such as polyacrylic acids, polymethacrylic acid or polymaleic acids, or polymeric sulfonic acids, such as polystyrene sulfonic acids and polyvinylsulfonic acids. These polycarbonic and sulfonic acids can also be copolymers of vinylcarbonic and vinyl sulfonic acids with other polymerizable monomers, such as acrylic acid esters and styrene.

Monomeric anions are preferably used for the solid electrolyte, since these penetrate better into the oxidized electrode body.

Examples of monomeric anions are those of C.₁-C₂₀Alkanesulfonic acids, such as methane, ethane, propane, butane or higher sulfonic acids such as dodecanesulfonic acid, from aliphatic perfluorosulfonic acids, such as trifluoromethanesulfonic acid, perfluorobutanesulfonic acid or perfluorooctanesulfonic acid, from aliphatic C.₁-C₂₀-Carboxylic acids such as 2-ethylhexylcarboxylic acid, aliphatic perfluorocarboxylic acids such as trifluoroacetic acid or perfluorooctanoic acid, and aromatic, optionally by C₁-C₂₀-Alkyl groups-substituted sulfonic acids such as benzenesulfonic acid, o-toluenesulfonic acid, p-toluenesulfonic acid or dodecylbenzenesulfonic acid and of cycloalkanesulfonic acids such as camphorsulfonic acid or tetrafluoroborates, hexafluorophosphates, perchlorates, hexafluoroantimonates, hexafluoroarsenates or hexachloro-arsenates or hexachloro-arenates or hexachloro-arsenates or hexachloro-arenates.

The anions of p-toluenesulfonic acid, methanesulfonic acid or camphorsulfonic acid are preferred.

Cationic polythiophenes which contain anions as counterions for charge compensation are also often referred to in the technical field as polythiophene / (poly) anion complexes.

In addition to the conductive polymers and possibly also counterions, the solid electrolyte can contain binders, crosslinking agents, surface-active substances, such as ionic or nonionic surfactants or adhesion promoters and / or other additives.

Adhesion promoters are, for example, organofunctional silanes or their hydrolysates, for example 3-glycidoxypropyltrialkoxysilane, 3-aminopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-metacryloxypropyltrimethoxysilane, vinyltrimethoxysilane or octyltriethoxysilane.

The solid electrolyte preferably consists essentially of the conductive polymer and monomeric anions as counterions.

The solid electrolyte preferably forms a layer on the dielectric surface with a thickness of less than 200 nm, particularly preferably less than 100 nm, very particularly preferably less than 50 nm.

The coverage of the dielectric with the solid electrolyte is determined in the context of this invention as follows: The capacitance of the capacitor is measured in the dry and moist state at 120 Hz. The degree of coverage is the ratio of the capacity in the dry state to the capacity in the wet state expressed in percent. Dry condition means that the capacitor has been dried at elevated temperature (80-120 ° C) for several hours before being measured. Moist condition means that the condenser is exposed to saturated air humidity at elevated pressure, for example in a steam pressure boiler, for several hours. The moisture penetrates into pores that are not covered by the solid electrolyte and acts there as a liquid electrolyte.

The coverage of the dielectric by the solid electrolyte is preferably greater than 50%, particularly preferably greater than 70%, very particularly preferably greater than 80%.

The outer surface is understood to mean the outer sides of the capacitor body. According to the invention, as shown schematically and by way of example in FIG<figref idref="f0001">Fig. 1</figref> and <figref idref="f0002">Fig. 2</figref> shown, the polymeric outer layer.

<figref idref="f0001">Fig. 1</figref> describes a schematic representation of the structure of a solid electrolytic capacitor using the example of a tantalum capacitor<dl id="dl0002" compact="compact"><dt>1</dt><dd>Capacitor body</dd><dt>5</dt><dd>polymeric outer layer</dd><dt>6</dt><dd>Graphite / silver layer</dd><dt>7</dt><dd>Wire contact to the electrode body</dd><dt>8</dt><dd>contacts</dd><dt>9</dt><dd>encapsulation</dd><dt>10</dt><dd>Image section</dd></dl>

<figref idref="f0002">Fig. 2</figref> describes the enlarged image section 10 <figref idref="f0001">Fig. 1</figref> with the schematic layer structure of the tantalum capacitor<dl id="dl0003" compact="compact"><dt>10</dt><dd>Image section</dd><dt>2</dt><dd>porous electrode body</dd><dt>3</dt><dd>dielectric</dd><dt>4</dt><dd>Solid electrolyte</dd><dt>5</dt><dd>polymeric outer layer</dd><dt>6</dt><dd>Graphite / silver layer</dd></dl>reproduces.

In the following, a geometric surface is understood to mean the outer surface of the capacitor body, which results from the geometric dimensions. For cuboid sintered bodies, the geometric surface is therefore:<maths id="math0001" num=""><math display="block"><mi>G</mi><mi>e</mi><mi>O</mi><mi>m</mi><mi>e</mi><mi>t</mi><mi>r</mi><mi>i</mi><mi>s</mi><mi>c</mi><mi>H</mi><mi>e</mi><mi mathvariant="normal"></mi><mi mathvariant="italic">surface</mi><mo>=</mo><mn>2</mn><mfenced><mrow><mi mathvariant="bold">L</mi><mo>*</mo><mi>B</mi><mo>+</mo><mi mathvariant="bold">L</mi><mo>*</mo><mi>H</mi><mo>+</mo><mi mathvariant="bold">B</mi><mo>*</mo><mi>H</mi></mrow></mfenced><mo>,</mo></math><img file="EP1524678B2_D0002.tif" /></maths> where L is the length, B is the width and H is the height of the body and * is a multiplication sign. Only the part of the capacitor body on which the polymeric outer layer is located is considered.

If several capacitor bodies are used in one capacitor, the individual geometric surfaces add up to an overall geometric surface.

The dimensions of the developed film (length, width) are used as dimensions for solid electrolytic capacitors which contain, for example, a wound film as the porous electrode body.

Instead of solid electrolytes containing a conductive polymer, the solid electrolyte capacitors can also contain solid electrolytes containing a non-polymeric conductive material, such as charge transfer complexes such as TCNQ (7,7,8,8-tetracyano-1,4-quinodimethane), manganese dioxide or salts such as those that can form ionic liquids. With such solid electrolytic capacitors, too, the polymeric outer layer leads to lower residual currents.

For the polythiophenes with repeating units of the general formula (I), (II) or repeating units of the general formula (I) and (II), which are located in the polymeric outer layer, the same preferred ranges apply as for the polythiophenes in the solid electrolyte.

The polymeric anion can function as a counterion for the polyanilines and / or the polythiophenes with repeating units of the general formula (I), (II) or repeating units of the general formula (I) and (II). However, additional counterions can also be contained in the layer. However, the polymeric anion preferably serves as counterion in this layer.

Polymeric anions can, for example, anions of polymeric carboxylic acids, such as polyacrylic acids, polymethacrylic acid or polymaleic acids, or polymeric sulfonic acids, such as polystyrene sulfonic acids and polyvinylsulfonic acids. These polycarbonic and sulfonic acids can also be copolymers of vinylcarbonic and vinyl sulfonic acids with other polymerizable monomers, such as acrylic acid esters and styrene.

Preferred as the polymeric anion is an anion of a polymeric carbon or sulfonic acid.

The anion of polystyrene sulfonic acid (PSS) is particularly preferred as the polymeric anion.

The molecular weight of the polyacids providing the polyanions is preferably 1,000 to 2,000,000, particularly preferably 2,000 to 500,000. The polyacids or their alkali metal salts are commercially available, for example polystyrene sulfonic acids and polyacrylic acids, or else can be prepared by known processes (see, for example <nplcit id="ncit0001" npl-type="s"><text>Houben Weyl, Methods of Organic Chemistry, Vol. E 20 Macromolecular Substances, Part 2, (1987), p. 1141 uf</text></nplcit>.).

Polymer (s) anion (s) and polythiophene (s) and / or polyaniline (s) can in the polymeric outer layer in a weight ratio of 0.5: 1 to 50: 1, preferably from 1: 1 to 30: 1, particularly preferably 2: 1 to 20: 1 may be included. The weight of the polythiophenes and / or polyanilines corresponds to the weight of the monomers used, assuming that complete conversion takes place during the polymerization.

The polymeric outer layer can also contain monomeric anions. The same preferred ranges apply to the monomeric anions as listed above for the solid electrolyte.

The polymeric outer layer can also contain other components, such as surface-active substances, for example ionic and nonionic surfactants or adhesion promoters, such as, for example, organofunctional silanes or their hydrolysates, for example 3-glycidoxypropyltrialkoxysilane, 3-aminopropyltriethoxysilane, 3-mercaptopropyltrimethoxysiloxane, 3-metacryloxiloxane, 3-methacryloxiloxane, 3-methacryloxiloxane, 3-metacryloxiloxane, 3-methacryloxiloxane, 3-metacryloxiloxane, 3-metacryloxiloxane, 3-methacryloxiloxane, 3-metacryloxiloxane, 3-methacryloxiloxane, 3-metacryloxiloxane, 3-methacryloxiloxane, 3-methacryloxiloxane, 3-metacryloxiloxane, 3-methacryloxiloxane, 3-methacryloxiloxane, 3-methacryloxiloxane, 3-methacryloxiloxane, 3-methacryloxiloxane, 3-methacryloxiloxane, 3-methacryloxiloxane, 3-methacrylox Forx for example Octyltriethoxysilane.

The thickness of the polymeric outer layer is 1-1000 µm, preferably 1-100 µm, particularly preferably 2-50 µm, very particularly preferably 4-20 µm. The layer thickness can vary on the outer surface. In particular, the layer thickness at the edges of the capacitor body can be thicker or thinner than on the side surfaces of the capacitor body. An almost homogeneous layer thickness is preferred.

The composition of the polymeric outer layer can have a homogeneous or inhomogeneous distribution with regard to the composition of the polymeric organic binders, conductive polymers and polymeric anions. Homogeneous distributions are preferred.

The polymeric outer layer can be part of a multilayer system that forms the outer layer of the capacitor body. Thus, one or more further functional layers can be located between the solid electrolyte and the polymeric outer layer according to the invention. Further functional layers can also be located on the polymeric outer layer according to the invention. Furthermore, several polymeric outer layers according to the invention can be located on the capacitor body.

The polymeric outer layer is preferably located directly on the solid electrolyte. The polymeric outer layer preferably penetrates into the edge region of the capacitor body in order to achieve good electrical contact with the solid electrolyte and to increase the adhesion to the capacitor body, but not into the entire depth of all pores (cf. example<figref idref="f0002">Fig. 2</figref>).

In a particularly preferred embodiment, the electrolytic capacitor according to the invention contains a solid electrolyte containing poly (3,4-ethylenedioxythiophene) (PEDT) and a polymeric outer layer containing polystyrene sulfonic acid (PSS) and poly (3,4-ethylenedioxythiophene), the latter is often also described in the literature as Designated PEDT / PSS or PEDOT / PSS.

In a very particularly preferred embodiment, the electrolytic capacitor according to the invention contains a solid electrolyte made of poly (3,4-ethylenedioxythiophene) and monomeric counterions and a polymeric outer layer made of PEDT / PSS and a polymeric organic binder.

The present invention further preferably relates to an electrolytic capacitor according to the invention, characterized in that the electrode material is a valve metal or a compound with comparable properties.

In the context of the invention, valve metal is to be understood as those metals whose oxide layers do not allow the current to flow in both directions equally: When the voltage is applied anodically, the oxide layers of the valve metals block the current flow, while when the voltage is applied cathodically, large currents occur which destroy the oxide layer can. The valve metals include Be, Mg, Al, Ge, Si, Sn, Sb, Bi, Ti, Zr, Hf, V, Nb, Ta and W and an alloy or combination of at least one of these metals with other elements. The best known representatives of the valve metals are Al, Ta, and Nb. Compounds with comparable properties are those with metallic conductivity, which can be oxidized and whose oxide layers have the properties described above. For example, NbO has metallic conductivity, but is generally not considered a valve metal. However, layers of oxidized NbO have the typical properties of valve metal oxide layers, so that NbO or an alloy or compound of NbO with other elements are typical examples of such compounds with comparable properties.

Accordingly, the term "oxidizable metal" means not only metals, but also an alloy or compound of a metal with other elements, provided that they have metallic conductivity and are oxidizable.

Accordingly, the present invention particularly preferably relates to an electrolytic capacitor, characterized in that the valve metal or the compound with comparable properties is tantalum, niobium, aluminum, titanium, zirconium, hafnium, vanadium, an alloy or compound of at least one of these metals with other elements, NbO or an alloy or compound of NbO with other elements.

The dielectric preferably consists of an oxide of the electrode material. It may contain other elements and / or compounds.

In addition to the type of dielectric, the capacitance of the oxidized electrode body depends on the surface and the thickness of the dielectric. The specific charge is a measure of how much charge per unit weight the oxidized electrode body can hold. The specific charge is calculated as follows:<maths id="math0002" num=""><math display="block"><mi mathvariant="bold">Specific</mi><mi mathvariant="italic"> charge</mi><mo>=</mo><mfenced><mrow><mi mathvariant="bold">capacity</mi><mo>*</mo><mi mathvariant="italic">tension</mi></mrow></mfenced><mo>/</mo><mi mathvariant="bold">Weight</mi><mi mathvariant="italic"> of the oxidized electrode body</mi><mo>.</mo></math><img file="EP1524678B2_D0003.tif" /></maths>

The capacitance results from the capacitance of the finished capacitor measured at 120 Hz and the voltage is the working voltage of the capacitor (rated voltage). The weight of the oxidized electrode body refers to the pure weight of the porous electrode material coated with dielectric without polymer, contacts and encapsulations.

The electrolytic capacitors according to the invention preferably have a specific charge greater than 10,000 μC / g, particularly preferably greater than 20,000 μC / g, very particularly preferably greater than 30,000 μC / g, very preferably greater than 40,000 μC / g.

The solid electrolytic capacitor according to the invention is characterized by low residual currents and a low equivalent series resistance. Since the polymeric outer layer forms a tight layer around the capacitor body and its edges are very well covered, the capacitor body is robust against mechanical loads. In addition, the polymeric outer layer shows good adhesion to the capacitor body and high electrical conductivity, so that low equivalent series resistances can be achieved.

A preferred subject of the present invention are electrolytic capacitors which have an ESR measured at 100 kHz of less than 51 mΩ. The ESR of the electrolytic capacitors according to the invention, which is measured at a frequency of 100 kHz, is particularly preferably less than 31 mΩ, very particularly preferably less than 21 mΩ, very preferably less than 16 mΩ. In particularly preferred embodiments of the electrolytic capacitors according to the invention, the ESR is less than 11 mΩ.

The equivalent series resistance of a solid electrolytic capacitor correlates inversely with the geometric surface of the capacitor. The product of the equivalent series resistance and the geometric surface therefore indicates a size that is independent of the size.

The present invention therefore also preferably relates to electrolytic capacitors in which the product of the equivalent series resistance measured at 100 kHz and the geometric surface of the capacitor body is less than 4000 mΩmm² is. The product of the equivalent series resistance and the geometric surface area of ​​less than 3000 mΩmm is particularly preferred², very particularly preferably less than 2000 mΩmm², very preferably less than 1000 mΩmm². In particularly preferred embodiments of the electrolytic capacitors according to the invention, the product of the equivalent series resistance and the geometric surface area is less than 600 mΩmm².

In principle, such an electrolytic capacitor according to the invention is manufactured as follows: First, for example, a powder with a high surface area is pressed and sintered to form a porous electrode body. Metal foils can also be etched to obtain a porous foil. The electrode body is then coated, for example by electrochemical oxidation, with a dielectric, ie an oxide layer. A conductive polymer, which forms the solid electrolyte, is deposited chemically or electrochemically on the dielectric by means of oxidative polymerization. A layer containing at least one polymeric anion and at least one optionally substituted polyaniline and / or a polythiophene with recurring units of the general formula (I), (II) or recurring units of the general formula ( I) and (II), and at least one polymeric organic binder applied from a dispersion. If necessary, further layers are applied to the polymeric outer layer. A coating with highly conductive layers, such as graphite and silver, or a metallic cathode body serves as an electrode for dissipating the current. Finally, the capacitor is contacted and encapsulated.

The present invention thus furthermore relates to a process for producing an electrolytic capacitor according to the invention, according to which the solid electrolyte containing at least one conductive polymer is produced by precursors for producing conductive polymers, one or more oxidizing agents and optionally counterions, together or in succession, if appropriate in the form of solutions, applied to a dielectric of a porous electrode body, optionally covered with further layers, and polymerized chemically oxidatively at temperatures from -10 ° C. to 250 ° C., or that precursors for the production of conductive polymers and counterions, if appropriate from solution, by electrochemical polymerization at temperatures of - 78 ° C. to 250 ° C. are polymerized on a dielectric of a porous electrode body, optionally covered with further layers, and the layer containing at least one polymeric anion and at least one optionally substituted polyaniline and / or at least one polythiophene with repeating units of the general formula (I), (II) or repeating units of the general formula (I) and (II),<chemistry id="chem0002" num="0002"><img file="EP1524678B2_D0004.tif" /></chemistry>wherein<dl id="dl0004" compact="compact"><dt>A, R and x</dt><dd>have the meaning given above for the general formulas (I) and (II),</dd></dl>and at least one polymeric organic binder from a dispersion comprising at least one polymeric anion and at least one optionally substituted polyaniline and / or at least one polythiophene with repeating units of the general formula (I), (II) or repeating units of the general formula (I) and ( II) and at least one polymeric organic binder is applied.

Corresponding monomers or their derivatives are understood as precursors for the production of conductive polymers, also referred to below as precursors. Mixtures of different precursors can also be used. Suitable monomeric precursors are, for example, optionally substituted thiophenes, pyrroles or anilines, preferably optionally substituted thiophenes, particularly preferably optionally substituted 3,4-alkylenedioxythiophenes.

Examples of substituted 3,4-alkylenedioxythiophenes are the compounds of the general formula (III), (IV) or a mixture of thiophenes of the general formulas (III) and (IV),<chemistry id="chem0003" num="0003"><img file="EP1524678B2_D0005.tif" /></chemistry>listed, wherein<dl id="dl0005"><dt>A</dt><dd>for an optionally substituted C₁-C₅Alkylene radical, preferably for an optionally substituted C₂-C₃Alkylene radical,</dd><dt>R</dt><dd>for a linear or branched, optionally substituted C₁-C₁₈-Alkylrest, preferably linear or branched, optionally substituted C₁-C₁₄Alkyl radical, an optionally substituted C₅-C₁₂-Cycloalkylrest, an optionally substituted C₆-C₁₄Aryl radical, an optionally substituted C₇-C₁₈Aralkyl radical, an optionally substituted C₁-C₄-Hydroxyalkylrest, preferably optionally substituted C₁-C₂-Hydroxyalkyl radical, or a hydroxyl radical,</dd><dt>x</dt><dd>represents an integer from 0 to 8, preferably from 0 to 6, particularly preferably 0 or 1 and</dd></dl>in the event that several R radicals are bonded to A, these may be the same or different,

Particularly preferred monomeric precursors are optionally substituted 3,4-ethylenedioxythiophenes.

Examples of substituted 3,4-ethylenedioxythiophenes are the compounds of the general formula (V)<chemistry id="chem0004" num="0004"><img file="EP1524678B2_D0006.tif" /></chemistry>wherein<dl id="dl0006" compact="compact"><dt>R and x</dt><dd>have the meaning given for the general formulas (III) and (IV).</dd></dl>

In the context of the invention, derivatives of these monomeric precursors are understood to mean, for example, dimers or trimers of these monomeric precursors. Higher molecular weight derivatives, ie tetramers, pentamers etc. of the monomeric precursors are also possible as derivatives.

Examples of derivatives of substituted 3,4-alkylenedioxythiophenes are the compounds of the general formula (VI)<chemistry id="chem0005" num="0005"><img file="EP1524678B2_D0007.tif" /></chemistry>wherein<ul id="ul0001" list-style="none"><li>n represents an integer from 2 to 20, preferably 2 to 6, particularly preferably 2 or 3, and</li><li>A, R and x have the meaning given for the general formulas (III) and (IV).</li></ul>

The derivatives can be constructed from the same or different monomer units and can be used in pure form and in a mixture with one another and / or with the monomeric precursors. Oxidized or reduced forms of these precursors are also included in the sense of the invention by the term "precursors", provided that the same conductive polymers are formed in their polymerization as in the precursors listed above.

The substituents mentioned for the general formulas (III) and (IV) for R are suitable as substituents for the precursors, in particular for the thiophenes, preferably for the 3,4-alkylenedioxythiophenes.

The C₁-C₅Alkylene radicals A and the optionally further substituents of the C₁-C₅-Alkylene radicals A correspond to those listed above for the polymers of the general formulas (I) and (II).

Processes for the preparation of the monomeric precursors for the production of conductive polymers and their derivatives are known to the person skilled in the art and are described, for example, in <nplcit id="ncit0002" npl-type="s"><text>L. Groenendaal, F. Jonas, D. Freitag, H. Pielartzik &amp; JR Reynolds, Adv. Mater. 12 (2000) 481-494</text></nplcit> and literature cited therein.

The 3,4-alkyleneoxythiathiophenes of the formula (III) required for the preparation of the polythiophenes to be used are known to the person skilled in the art or can be prepared by known processes (for example according to <nplcit id="ncit0003" npl-type="s"><text>P. Blanchard, A. Cappon, E. Levillain, Y. Nicolas, P. Frère and J. Roncali, Org. Lett. 4 (4), 2002, pp. 607-609</text></nplcit>).

The conductive polymers are produced on the electrode body covered with a dielectric by oxidative polymerization of precursors for the production of conductive polymer by applying the precursors, oxidizing agents and optionally counterions, preferably in the form of solutions, either separately in succession or together on the dielectric of the electrode body and the oxidative polymerization, depending on the activity of the oxidizing agent used, optionally by heating the coating.

The application can be carried out directly or using an adhesion promoter, for example a silane, such as, for example, organofunctional silanes or their hydrolyzates, for example 3-glycidoxypropyltrialkoxysilane, 3-aminopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-metacryloxypropyltrimethoxysilane or vinylanimoxysilane or vinylanimoxysilane or vinylanimoxysilane or vinylanimoxysilane or vinylanimoxysilane or vinylanimoxysilane several other functional layers on the dielectric of the electrode body.

Depending on the oxidizing agent used and the desired reaction time, the oxidative chemical polymerization of the thiophenes of the formula (s) (III) or (IV) is generally carried out at temperatures from -10 ° C. to 250 ° C., preferably at temperatures from 0 ° C. to 200 ° C, made.

The following may be mentioned as solvents for the precursors for the production of conductive polymers and / or oxidizing agents and / or counterions, in particular the following organic solvents which are inert under the reaction conditions: aliphatic alcohols such as methanol, ethanol, i-propanol and butanol; aliphatic ketones such as acetone and methyl ethyl ketone; aliphatic carboxylic acid esters such as ethyl acetate and butyl acetate; aromatic hydrocarbons such as toluene and xylene; aliphatic hydrocarbons such as hexane, heptane and cyclohexane; Chlorinated hydrocarbons such as dichloromethane and dichloroethane; aliphatic nitriles such as acetonitrile, aliphatic sulfoxides and sulfones such as dimethyl sulfoxide and sulfolane; aliphatic carboxamides such as methylacetamide, dimethylacetamide and dimethylformamide; aliphatic and araliphatic ethers such as diethyl ether and anisole. Furthermore, water or a mixture of water with the aforementioned organic solvents can also be used as the solvent.

All metal salts known to the person skilled in the art and suitable for the oxidative polymerization of thiophenes, anilines or pyrroles can be used as the oxidizing agent.

Suitable metal salts are metal salts of main or subgroup metals, the latter also referred to below as transition metal salts, of the periodic table of the elements. Suitable transition metal salts are, in particular, salts of an inorganic or organic acid or inorganic acid having organic residues of transition metals, such as iron (III), copper (II), chromium (VI), cerium (IV), manganese (IV), manganese (VII ) and ruthenium (III).

Preferred transition metal salts are those of iron (III). Conventional iron (III) salts are advantageously inexpensive, readily available and can be handled easily, such as, for example, the iron (III) salts of inorganic acids, such as, for example, iron (III) halides (for example FeCl₃) or iron (III) salts of other inorganic acids, such as Fe (ClO₄)₃ or Fe₂(SO₄)₃, and the iron (III) salts of organic acids and organic residues containing inorganic acids.

Examples of iron (III) salts of organic residues containing inorganic acids are the iron (III) salts of the sulfuric acid monoesters of C₁-C₂₀Alkanols, for example the iron (III) salt of lauryl sulfate.

Particularly preferred transition metal salts are those of an organic acid, in particular iron (III) salts of organic acids.

Examples of iron (III) salts of organic acids are: the iron (III) salts of C₁-C₂₀Alkanesulfonic acids, such as methane, ethane, propane, butane or higher sulfonic acids such as dodecanesulfonic acid, of aliphatic perfluorosulfonic acids, such as trifluoromethanesulfonic acid, perfluorobutanesulfonic acid or perfluorooctane sulfonic acid, of aliphatic C₁-C₂₀-Carboxylic acids such as 2-ethylhexylcarboxylic acid, aliphatic perfluorocarboxylic acids such as trifluoroacetic acid or perfluorooctanoic acid, and aromatic, optionally by C₁-C₂₀-Alkyl groups-substituted sulfonic acids such as benzenesulfonic acid, o-toluenesulfonic acid, p-toluenesulfonic acid or dodecylbenzenesulfonic acid and cycloalkanesulfonic acids such as camphorsulfonic acid.

Any mixtures of these aforementioned iron (III) salts of organic acids can also be used.

The use of the iron (III) salts of organic acids and the inorganic acids containing organic residues has the great advantage that they do not have a corrosive effect.

Iron (III) -p-toluenesulfonate, iron (III) -o-toluenesulfonate or a mixture of iron (III) -p-toluenesulfonate and iron (III) -o-toluenesulfonate are very particularly preferred as metal salts.

In preferred embodiments, the metal salts have been treated with an ion exchanger, preferably a basic anion exchanger, before being used. Examples of suitable ion exchangers are macroporous polymers of styrene and divinylbenzene functionalized with tertiary amines, such as those sold under the trade name Lewatit® by Bayer AG, Leverkusen. The production of such metal salts treated with an ion exchanger is shown in<patcit id="pcit0008" dnum="DE10324534"><text>DE 103 24 534</text></patcit> described.

Other suitable oxidizing agents are peroxo compounds such as peroxodisulfates (persulfates), in particular ammonium and alkali peroxodisulfates, such as sodium and potassium peroxodisulfate, or alkali perborates - optionally in the presence of catalytic amounts of metal ions, such as iron, cobalt, nickel, molybdenum or vanadium ions, and Transition metal oxides such as manganese dioxide (manganese (IV) oxide) or cerium (IV) oxide.

For the oxidative polymerization of the thiophenes of the formula (III) or (IV), 2.25 equivalents of oxidizing agents are theoretically required per mole of thiophene (see, for example <nplcit id="ncit0004" npl-type="s"><text>J. Polym. Sc. Part A Polymer Chemistry Vol. 26, p. 1287 (1988</text></nplcit>)). However, lower or higher equivalents of oxidizing agent can also be used. In the context of the invention, preferably one equivalent or more, particularly preferably 2 equivalents or more, of oxidizing agent is used per mole of thiophene.

If the precursors, oxidizing agents and optionally counterions are applied separately, the dielectric of the electrode body is preferably first coated with the solution of the oxidizing agent and optionally the counterions and then with the solution of the precursors. In the preferred joint application of precursors, oxidizing agents and optionally counterions, the dielectric of the electrode body is coated with only one solution, namely a solution containing precursors, oxidizing agents and optionally counterions.

The solutions can also contain other components such as one or more organic binders which are soluble in organic solvents, such as polyvinyl acetate, polycarbonate, polyvinyl butyral, polyacrylic acid esters, polymethacrylic acid esters, polystyrene, polyacrylonitrile, polyvinyl chloride, polybutadiene, polyisoprene, polyethers, polyesters, silicones, styrene / acrylic acid esters, vinyl acetate / Acrylic acid ester and ethylene / vinyl acetate copolymers or water-soluble binders such as polyvinyl alcohols, Crosslinkers such as melamine compounds, masked isocyanates, functional silanes - for example tetraethoxysilane, alkoxysilane hydrolyzates, for example based on tetraethoxysilane, epoxysilanes such as 3-glycidoxypropyltrialkoxysilane - polyurethanes, polyacrylates or polyolefin dispersions, and / or additives, for example surfactants, for example ionic surfactants, for example ionic surfactants such as organofunctional silanes or their hydrolyzates, for example 3-glycidoxypropyltrialkoxysilane, 3-aminopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-metacryloxypropyltrimethoxysilane, vinyltrimethoxysilane, octyltriethoxysilane. be added.

The solutions to be applied to the dielectric of the electrode body preferably contain 1 to 30% by weight of the thiophene of the general formula (III) or the mixture of thiophenes of the general formulas (III) and (IV) and 0 to 50% by weight of binder, Crosslinker and / or additives, both percentages by weight based on the total weight of the mixture.

The solutions are applied to the dielectric of the electrode body by known processes, for example by impregnation, pouring, dropping, spraying, spraying, knife coating, brushing, spin coating or printing, for example ink-jet, screen, contact or pad printing.

The solvents can be removed after the solutions have been applied by simple evaporation at room temperature. However, in order to achieve higher processing speeds, it is more advantageous to remove the solvents at elevated temperatures, for example at temperatures from 20 to 300 ° C., preferably 40 to 250 ° C. A thermal aftertreatment can be connected directly with the removal of the solvent or can also be carried out at an interval from the completion of the coating.

The duration of the heat treatment is 5 seconds to several hours, depending on the type of polymer used for the coating. Temperature profiles with different temperatures and residence times can also be used for the thermal treatment.

The heat treatment can be carried out, for example, by moving the coated, oxidized electrode bodies at such a speed through a heating chamber at the desired temperature that the desired dwell time at the selected temperature is achieved, or with a heating plate at the desired temperature for the desired dwell time. Furthermore, the heat treatment can be carried out, for example, in a heating oven or a plurality of heating ovens, each with different temperatures.

After removing the solvents (drying) and, if appropriate, after the thermal aftertreatment, it may be advantageous to wash out the excess oxidizing agent and residual salts from the coating with a suitable solvent, preferably water or alcohols. Residual salts are to be understood here as the salts of the reduced form of the oxidizing agent and, if appropriate, other salts present.

For metal oxide dielectrics, such as the oxides of the valve metals, it can be advantageous after the polymerization and preferably during or after washing to electrochemically simulate the oxide film in order to repair any imperfections in the oxide film and thereby reduce the residual current in the finished capacitor. In this so-called reforming, the capacitor body is immersed in an electrolyte and a positive voltage is applied to the electrode body. The flowing current simulates the oxide at defective locations in the oxide film or destroys conductive polymer at imperfections through which a high current flows.

Depending on the type of the oxidized electrode body, it may be advantageous to impregnate the oxidized electrode body with the mixtures a further number of times, preferably after washing, in order to achieve thicker polymer layers.

The polythiophenes can also be prepared from the precursors by electrochemical oxidative polymerization.

In the case of electrochemical polymerization, the electrode body coated with a dielectric can first be coated with a thin layer of a conductive polymer. After a voltage is applied to this layer, the layer containing the conductive polymer grows thereon. Other conductive layers can also be used as the deposition layer. Describe like this<nplcit id="ncit0005" npl-type="s"><text>Y. Kudoh et al. in Journal of Power Sources 60 (1996) 157-163</text></nplcit> the use of a manganese oxide deposition layer.

The electrochemical oxidative polymerization of the precursors can be carried out at temperatures from -78 ° C to the boiling point of the solvent used. Is preferably electrochemically polymerized at temperatures from -78 ° C to 250 ° C, particularly preferably from -20 ° C to 60 ° C.

Depending on the precursor used, the electrolyte used, the temperature selected and the current density used, the reaction times are 1 minute to 24 hours.

If the precursors are liquid, the electropolymerization can be carried out in the presence or absence of solvents which are inert under the conditions of the electropolymerization; the electropolymerization of solid precursors is carried out in the presence of solvents which are inert under the conditions of the electrochemical polymerization. In certain cases it can be advantageous to use solvent mixtures and / or to add solubilizers (detergents) to the solvents.

Examples of solvents which are inert under the conditions of electropolymerization are: water; Alcohols such as methanol and ethanol; Ketones such as acetophenone; halogenated hydrocarbons such as methylene chloride, chloroform, carbon tetrachloride and fluorocarbons; Esters such as ethyl acetate and butyl acetate; Carbonic acid esters such as propylene carbonate; aromatic hydrocarbons such as benzene, toluene, xylene; aliphatic hydrocarbons such as pentane, hexane, heptane and cyclohexane; Nitriles such as acetonitrile and benzonitrile; Sulfoxides such as dimethyl sulfoxide; Sulfones such as dimethyl sulfone, phenylmethyl sulfone and sulfolane; liquid aliphatic amides such as methylacetamide, dimethylacetamide, dimethylformamide, pyrrolidone, N-methylpyrrolidone, N-methylcaprolactam; aliphatic and mixed aliphatic-aromatic ethers such as diethyl ether and anisole; liquid ureas such as tetramethyl urea or N, N-dimethyl-imidazolidinone.

For the electropolymerization, the precursors or their solutions are mixed with electrolyte additives. Free acids or conventional conductive salts which have a certain solubility in the solvents used are preferably used as electrolyte additives. As electrolyte additives have, for example proven: free acids such as p-toluenesulfonic acid, methanesulfonic acid, also salts with alkanesulfonate, aromatic sulfonate, tetrafluoroborate, hexafluorophosphate, perchlorate, hexafluoroantimonate, hexafluoroarsenate and hexachloroantimonate anions and optionally alkali metal or alkaline earth metal, alkaline earth metal , Phosphonium, sulfonium and oxonium cations.

The concentrations of the precursors can be between 0.01 and 100% by weight (100% by weight only in the case of a liquid precursor); the concentrations are preferably 0.1 to 20% by weight.

The electropolymerization can be carried out batchwise or continuously.

The current densities for electropolymerization can vary within wide limits; Usually with current densities of 0.0001 to 100 mA / cm², preferably 0.01 to 40 mA / cm² worked. At these current densities, voltages of approximately 0.1 to 50 V are established.

For metal oxide dielectrics, it can be advantageous after electrochemical polymerization to electrochemically simulate the oxide film in order to repair any imperfections in the oxide film and thereby reduce the residual current of the finished capacitor (reforming).

Suitable counterions are the monomeric or polymeric anions already listed above, preferably those of the monomeric or polymeric alkane or cycloalkane sulfonic acids or aromatic sulfonic acids. The anions of the monomeric alkane or cycloalkanesulfonic acids or aromatic sulfonic acids are particularly preferred for use in the electrolytic capacitors according to the invention, since solutions containing them are more suitable for penetrating into the porous electrode material coated with a dielectric, and thus a larger contact area is formed between the latter and the solid electrolyte can be. The counterions are added to the solutions, for example in the form of their alkali salts or as free acids. In the case of electrochemical polymerization, these counterions are optionally added to the solution or the thiophenes as electrolyte additives or conductive salts.

In addition, the anions of the oxidizing agent that may be present can serve as counterions, so that in the case of chemical oxidative polymerization it is not absolutely necessary to add additional counterions.

After the production of the solid electrolyte and optionally after the application of further layers to the capacitor body, the layer containing at least one polymeric anion and at least one optionally substituted polyaniline and / or a polythiophene with repeating units of the general formula (I), (II) or repeating units of the general Formulas (I) and (II),<chemistry id="chem0006" num="0006"><img file="EP1524678B2_D0008.tif" /></chemistry>wherein<dl id="dl0007" compact="compact"><dt>A, R and x</dt><dd>have the meaning given above for the general formulas (I) and (II),</dd></dl>as well as at least one polymeric organic binder from a dispersion comprising at least one polymeric anion and at least one optionally substituted polyaniline and / or a polythiophene with repeating units of the general formula (I), (II) or repeating units of the general formula (I) and (II ) and at least one polymeric organic binder applied.

The dispersions can also contain one or more solvents. Suitable solvents are those mentioned above for the precursors. Preferred solvents are water or other protic solvents such as alcohols, for example methanol, ethanol, i-propanol and butanol, and mixtures of water with these alcohols, water is a particularly preferred solvent.

Possible polymeric anions and polymeric organic binders in the polymeric outer layer are those which have already been mentioned above in connection with the electrolytic capacitor according to the invention. Preferred ranges apply in any combination.

The addition of polymeric organic binders has the great advantage that the adhesion of the outer polymer layer to the capacitor body is increased. In addition, the polymeric organic binder increases the solids content in the dispersion, so that a sufficient outer layer thickness can be achieved with an impregnation and the edge coverage is significantly improved.

For the polythiophenes with recurring units of the general formula (I) and / or (II) in the polymeric outer layer, the above applies in connection with the electrolytic capacitor according to the invention. Preferred ranges apply in any combination.

The dispersions containing at least one polymeric anion and optionally substituted polyaniline and / or at least one polythiophene with repeating units of the general formula (I), (II) or repeating units of the general formula (I) and (II) can also contain crosslinkers, surface-active substances, such as ionic or nonionic surfactants or adhesion promoters, and / or additives. The above-mentioned can be used as crosslinkers, surface-active substances and / or additives.

The dispersions can also contain monomeric anions.

The dispersions preferably contain further additives which increase the conductivity, such as, for example, compounds containing ether groups, such as Tetrahydofuran, compounds containing lactone groups such as γ-butyrolactone, γ-valerolactone, compounds containing amide or lactam groups such as caprolactam, N-methylcaprolactam, N, N-dimethylacetamide, N-methylacetamide, N, N-dimethylformamide (DMF), N-methylformamide, N- Methylformanilide, N-methylpyrrolidone (NMP), N-octylpyrrolidone, pyrrolidone, sulfones and sulfoxides such as sulfolane (tetramethylene sulfone), dimethyl sulfoxide (DMSO), sugar or sugar derivatives such as Sucrose, glucose, fructose, lactose, sugar alcohols such as sorbitol, mannitol, furan derivatives such as 2-furan carboxylic acid, 3-furan carboxylic acid, and / or di- or polyalcohols such as ethylene glycol, glycerol, di- or

Triethylene glycol ,. Tetrahydrofuran, N-methylformamide, N-methylpyrrolidone, dimethyl sulfoxide or sorbitol are particularly preferably used as conductivity-increasing additives.

The dispersions are prepared from optionally substituted anilines, thiophenes of the general formula (III), (IV) or mixtures of thiophenes of the general formulas (III) and (IV), for example analogously to those in <patcit id="pcit0009" dnum="EP440957A"><text>EP-A 440 957</text></patcit> conditions mentioned. Possible oxidizing agents, solvents and polymeric anions are those already listed above.

A preparation of the polyaniline / polyanion or polythiophene / polyanion complex and subsequent dispersion or redispersion in one or more solvents is also possible.

The dispersions are applied to the capacitor body by known methods, for example by spin coating, impregnation, pouring, dripping, spraying, spraying, knife coating, brushing or printing, for example ink-jet, screen or pad printing.

Depending on the type of application, the viscosity of the dispersion can be between 0.1 and 100,000 mPa · s. The viscosity is preferably 1 to 10,000 mPa · s, particularly preferably between 10 to 1000 mPa · s, very particularly preferably 30-500 mPa · s.

When the dispersion is applied to the capacitor body by means of impregnation, it may be advantageous to have a thin film of higher viscosity formed on the surface of the dispersion before the impregnation. If the capacitor body is then gradually immersed in such a dispersion in one or more impregnation and drying cycles, the coverage of the edges and corners of the capacitor body is significantly improved and bubbles are prevented from forming in the dry polymer film. For example, only half of the capacitor body can be soaked in the dispersion in the first step and then dried. In a second impregnation step, the capacitor body can then be completely immersed in the dispersion and then dried. The formation of the thin film of higher viscosity on the surface of the dispersion can be achieved, for example, by simply standing in an open atmosphere. For example, film formation can be accelerated by heating the dispersion or by heating the dispersion surface with warm air or heat radiation.

Dispersions containing at least one polymeric anion and optionally substituted polyaniline and / or at least one polythiophene with repeating units of the general formula (I), (II) or repeating units of the general formula (I) and (II) are preferably used in the dried state have a specific conductivity of greater than 10 S / cm, particularly preferably greater than 20 S / cm, very particularly preferably greater than 50 S / cm and very preferably greater than 100 S / cm.

The application of the polymeric outer layer can also be followed by drying, cleaning of the layer by washing, reforming and repeated application - as already described above for the production of the solid electrolyte. Depending on the polymeric organic binder or crosslinking agent used, further treatment steps such as curing or crosslinking by temperature or light can also be used. Furthermore, further layers can be applied to the polymeric outer layer.

Surprisingly, it was found that no further treatment steps of the layer are required for metal-oxide dielectrics after application and drying of the dispersion in order to produce solid electrolytic capacitors with low ESR and low residual current. In other methods for producing a polymeric outer layer, the oxide layer usually has to be reformed after application of the conductive polymeric outer layer in order to achieve low residual currents. This reforming in an electrolyte allows the polymeric outer layer to detach locally from the capacitor body, which increases the ESR. When using the method according to the invention, the reforming can be omitted without increasing the residual current.

The valve metals or compounds with comparable properties listed above for the electrolytic capacitor are preferably used to produce the electrode body. Preferred areas apply accordingly.

The oxidizable metals are, for example, sintered in powder form to form a porous electrode body, or a porous structure is impressed on a metallic body. The latter can be done, for example, by etching a film.

The porous electrode bodies are, for example, oxidized in a suitable electrolyte, such as phosphoric acid, by applying a voltage. The level of this forming voltage depends on the oxide layer thickness to be achieved or the later application voltage of the capacitor. Preferred voltages are 1 to 300 V, particularly preferably 1 to 80 V.

Metal powders with a specific charge greater than 35000 µC / g, particularly preferably with a specific charge greater than 45000 µC / g, very particularly preferably with a specific charge greater than 65000 µC / g, most preferably with a specific charge greater are preferred for producing the electrode body 95000 µC / g used. In preferred embodiments of the method according to the invention, metal powders with a specific charge greater than 140,000 μC / g are used.

The specific charge is calculated as follows: <maths id="math0003" num=""><math display="block"><mi mathvariant="bold">Specific</mi><mi mathvariant="italic"> charge</mi><mo>=</mo><mfenced><mrow><mi mathvariant="bold">capacity</mi><mo>*</mo><mi mathvariant="bold">tension</mi></mrow></mfenced><mo>/</mo><mi mathvariant="bold">Weight</mi><mi mathvariant="italic"> of the oxidized electrode body</mi><mo>.</mo></math><img file="EP1524678B2_D0009.tif" /></maths>

The capacity results from the capacity of the oxidized electrode body measured at 120 Hz in an aqueous electrolyte. The electrical conductivity of the electrolyte is sufficiently large that there is not yet a decrease in capacitance at 120 Hz due to the electrical resistance of the electrolyte. For example, 18% aqueous sulfuric acid electrolytes are used for the measurement. The tension in the above formula corresponds to the maximum forming tension (oxidation tension).

With the method according to the invention, solid electrolyte capacitors with a dense polymeric outer layer, which have good edge coverage and adhesion, can be produced in a particularly simple manner. The capacitors are characterized by low residual currents and a low ESR.

Due to their low residual current and their low ESR, the electrolytic capacitors according to the invention and the electrolytic capacitors produced according to the invention are outstandingly suitable as a component in electronic circuits. Preferred are digital electronic circuits, such as those found in computers (desktop, laptop, server), in portable electronic devices, such as, for example, mobile telephones and digital cameras, in consumer electronics devices, such as, for example in CD / DVD players and computer game consoles, in navigation systems and in telecommunication facilities.

<u>Examples</u>

<u>example 1</u>:

Production of capacitors according to the invention

1. Manufacture of oxidized electrode bodies

Tantalum powder with a specific capacity of 50,000 µFV / g was pressed into pellets and sintered to form a porous electrode body with the dimensions 4.2 mm * 3 mm * 1.6 mm. The pellets (anode pellets) were anodized to 30 V in a phosphoric acid electrolyte.

2nd Chemical in-situ coating of the anode pellets

A solution consisting of one part by weight of 3,4-ethylenedioxythiophene (BAYTRON® M, HC Starck GmbH) and 20 parts by weight of a 40% by weight ethanolic solution of iron (III) p-toluenesulfonate (BAYTRON® CE, HC Starck GmbH).

The solution was used to impregnate 9 anode pellets. The anode pellets were soaked in this solution and then dried for 30 min at room temperature (20 ° C.). They were then heat-treated in a drying cabinet at 50 ° C. for 15 minutes and at 150 ° C. for 15 minutes. The pellets were then washed in water for 30 minutes. The anode pellet was reformed for 30 minutes in a 0.25% by weight aqueous solution of p-toluenesulfonic acid, then rinsed in distilled water and dried. The described impregnation, drying, temperature treatment and reforming were carried out two more times.

3rd Application of a polymeric outer layer

The anode pellets were then in an aqueous dispersion consisting of 90 parts of an aqueous PEDT / PSS dispersion (BAYTRON® P, HC Starck GmbH), 4 parts of NMP, 4.2 parts of a sulfonated polyester (Eastek® 1400, solids content. 30 wt. -% soaked in water, East-man) and 0.2 parts of surfactant (Zonyl® FS 300, Du Pont) and dried at 80 ° C for 15 min.

Finally, the pellets were coated with a graphite and silver layer.

The average of the 9 capacitors was as follows:<tables id="tabl0001" num="0001"><table frame="none"><tgroup cols="2" colsep="0" rowsep="0"><colspec colnum="1" colname="col1" colwidth="23mm" /><colspec colnum="2" colname="col2" colwidth="15mm" /><tbody><row><entry>Capacity:</entry><entry>147 µF</entry></row><row><entry>ISR:</entry><entry>26 mΩ</entry></row><row><entry>Residual current:</entry><entry>5 µA</entry></row></tbody></tgroup></table></tables>

The product of the geometric surface and ESR was 1250 mΩmm².

The capacitance was determined at 120 Hz and the equivalent series resistance (ESR) at 100 kHz using an LCR meter (Agilent 4284A). The residual current was determined three minutes after applying a 10 V voltage using a Keithley 199 multimeter.

<u>Example 2</u>:

Production of capacitors according to the invention

Tantalum powder with a specific capacity of 50,000 µFV / g was pressed into pellets and sintered to form a porous electrode body with the dimensions 4.2 mm * 3 mm * 0.8 mm. The pellets (anode pellets) were anodized to 30 V in a phosphoric acid electrolyte.

The chemical in-situ coating and the application of the polymeric outer layer was carried out according to Example 1 (steps 2 and 3).

After the polymer outer layer had been applied, the anode pellets were observed under a light microscope: the entire outer surface was covered with a dense polymer film. The edges also showed a continuous polymer film covering.

<figref idref="f0003">Fig. 3</figref> shows a light micrograph of a fracture surface of the capacitor according to the invention. An approximately 5-10 µm thick polymeric outer layer is clearly visible, which also envelops the edge of the capacitor pellet very well.

Two of the anode pellets were coated with a graphite and silver layer.

The capacitors according to the invention had an ESR of 15 mΩ on average. The product of the geometric surface and ESR was 551 mΩmm².

<u>Comparative Example 1</u>:

Production of capacitors not according to the invention without binders in the outer layer

9 capacitors were produced analogously to Example 1, but only the aqueous PEDT / PSS dispersion (BAYTRON® P, HC Starck GmbH) without binder and other additives was used for the polymeric outer layer. In order to achieve a sufficient layer thickness, the pellets were soaked twice and dried.

The polymer outer layer made of PEDT / PSS without binder flaked off when the graphite and silver layer was applied. All capacitors were electrically short-circuited and could no longer be measured.

The comparison with Example 1 shows that the addition of polymeric organic binder increases the adhesion of the polymeric outer layer to the porous capacitor body and thus enables capacitors with low residual currents.

<u>Comparative Example 2</u>:

Production of capacitors not according to the invention without in-situ polymerization

9 capacitors were manufactured analogously to Example 1, but no chemical in-situ coating was carried out (only 1st and 3rd steps from Example 1).

The capacitors had an average capacitance of only 0.9 µF. By contrast, the capacitors according to the invention from Example 1 had a capacitance of approximately 160 times higher at 147 μF. This shows that the PEDT / PSS penetrates into the porous structure only in the edge region of the capacitor body and the polymeric outer layer is essentially on the outer surface of the capacitor body.

<u>Comparative Example 3</u>:

Production of capacitors not according to the invention with an in-situ polymerized polymeric outer layer

<ol id="ol0001" ol-style=""><li>A) 9 capacitors were produced analogously to Example 1, but instead of the polymeric outer layer made of PEDT / PSS (3rd step in Example 1), an in-situ polymerized outer layer was produced by two further impregnation cycles (2nd step in Example 1 ) were made in addition, but without reforming. When a voltage of 10 V was applied, all capacitors were electrically short-circuited.</li><li>B) 9 capacitors were manufactured analogously to A), but with reforming in the two further impregnation cycles.</li></ol>

3rd of 9 capacitors were short-circuited, the remaining 6 showed a residual current of 1 µA on average at 10 V.

This example shows that in the case of outer layer formation by means of in-situ polymerization, reforming after application of the outer layer is necessary in order to achieve low residual currents. This reforming is not necessary for the capacitors according to the invention from Example 1. In addition, 33% of the capacitors from Example B were defective, while 100% of the capacitors according to the invention from Example 1 had low residual currents. The method according to the invention for producing capacitors is therefore not only simpler, but also more reliable. The yield of functional capacitors in the production process according to the invention is thus significantly higher.

<u>Example 3</u>:

Resistance of the capacitors according to the invention to mechanical loads

The capacitors according to the invention from Example 1 were placed on the silver layer using a metallic spring pin (spring force 3 N, round contact surface with a diameter of 1.5 mm, contact pressure approx. 170 N / cm² or 17 bar) for a residual current measurement.

The residual current at 10 V increased with this strong mechanical load from an average of 5 µA to 144 µA.

The capacitors from Example 4A not according to the invention with an in-situ polymerized outer layer were subjected to the same stress test. A 10 V voltage could not be applied to the 6 capacitors with a residual current of 1 µA from Example 4A without generating electrical short circuits. At 0.5 V, the capacitors already showed an average residual current of almost 2000 µA.

This example shows that the capacitors according to the invention have a high stability against mechanical loads.

<u>Example 4</u>:

Production of capacitors according to the invention with different polymeric dispersions

1. Manufacture of oxidized electrode bodies

Tantalum powder with a specific capacity of 50,000 µFV / g was pressed into pellets and sintered to form a porous electrode body with the dimensions 4.2 mm * 3 mm * 1.6 mm. The pellets (anode pellets) were anodized to 30 V in a phosphoric acid electrolyte.

2nd Chemical in-situ coating of the anode pellets

A solution consisting of one part by weight of 3,4-ethylenedioxythiophene (BAYTRON® M, HC Starck GmbH) and 20 parts by weight of a 40% by weight ethanolic solution of iron (III) p-toluenesulfonate (BAYTRON® CE, HC Starck GmbH).

The solution was used to impregnate 12 anode pellets. The anode pellets were soaked in this solution and then dried for 30 min at room temperature. They were then heat-treated in a drying cabinet at 50 ° C. for 15 minutes and at 150 ° C. for 15 minutes. The pellets were then washed in water for 30 minutes. The anode pellet was reformed for 30 minutes in a 0.25% by weight aqueous solution of p-toluic acid, then rinsed in distilled water and dried. The described impregnation, drying, temperature treatment and reforming were carried out two more times.

3rd Application of a polymeric outer layer

6 anode pellets each were then soaked in one of the following dispersions and then dried at 80 ° C. for 15 minutes:

Dispersion A:

90 Parts of an aqueous PEDT / PSS dispersion (BAYTRON® P, HC Starck GmbH), 4 parts of dimethyl sulfoxide (DMSO), 4.2 parts of a sulfonated polyester (Eastek® 1400, solids content. 30% by weight in water, Eastman) and 0 , 2 parts surfactant (Zonyl® FS 300, Du Pont)

Dispersion B:

90 Parts of an aqueous PEDT / PSS dispersion (BAYTRON® P, HC Starck GmbH), 4 parts of NMP, 4.2 parts of a sulfonated polyester (Eastek® 1400, solids content 30% by weight in water, Eastman) and 0.2 parts of surfactant (Zonyl® FS 300, Du Pont)

Finally, the pellets were coated with a graphite and silver layer.

The 6 capacitors each had the following electrical values ​​on average:<tables id="tabl0002" num="0002"><table frame="all"><tgroup cols="3"><colspec colnum="1" colname="col1" colwidth="27mm" /><colspec colnum="2" colname="col2" colwidth="23mm" /><colspec colnum="3" colname="col3" colwidth="23mm" /><thead><row><entry valign="top" /><entry valign="top">Dispersion A</entry><entry valign="top">Dispersion B</entry></row></thead><tbody><row><entry>ESR in mΩ</entry><entry>34</entry><entry>33</entry></row><row><entry>Residual current in µA</entry><entry>2,6</entry><entry>10</entry></row></tbody></tgroup></table></tables>

The equivalent series resistance (ESR) was determined at 100 kHz using an LCR meter (Agilent 4284A). The residual current was determined three minutes after applying a 10 V voltage using a Keithley 199 multimeter.

<u>Example 5</u>:

Temperature stability of the equivalent series resistance of capacitors according to the invention

4th Capacitors from Example 4, which were produced with dispersion B, were stored for 3 minutes at 260 ° C. in a drying cabinet.

The ESR after the temperature load was 32 mΩ on average. This shows that the capacitors according to the invention withstand typical temperature loads which occur when the capacitors are soldered onto printed circuit boards.

<u>Example 6:</u>

Production of a conductive layer

A conductive layer of dispersion B from example 4 was produced. For this purpose, part of the dispersion was spun onto a glass slide (26 mm * 26 mm * 1 mm) using a spin coater (Chemat Technology KW-4A) at 1000 rpm for 5 seconds. The sample was dried at 80 ° C for 15 minutes. Then two opposite edges of the slide were coated with conductive silver. After the conductive silver had dried, the two silver strips were contacted and the surface resistance was determined using a Keithley 199 multimeter. The layer thickness was determined using a Tencor Alpha Step 500 Surface Profiler. The specific conductivity was determined from the surface resistance and layer thickness. The layer thickness was 345 nm and the specific conductivity 55 S / cm.