DE102004030802B4 - Ceramic body coated with conductive polymers and method of manufacture - Google Patents

Abstract

dielectric ceramic body or body with a dielectric ceramic surface on which an electrical conductive Coating is arranged, which consists of several superimposed sub-layers a copolymer consisting of at least two different Monomers of pyrrole and thiophene and their derivatives based.

Description

Solid electrolytic capacitors such as tantalum capacitors include a porous one Anode body, which is connected to an electrode, and that of a dielectric coated layer is. The anode body is contacted by the electrode and puts together with this the anode of the electrolytic capacitor. On the surface of the dielectrically acting layer over the anode body an optionally multi-layer cathode is produced from conductive materials, usually by successive immersion, drying and pyrolysis processes.

Anodes for solid electrolytic capacitors are known in which the electrode body is a porous sintered body made of aluminum or a valve metal, in particular niobium or tantalum, and in which the dielectric layer is a layer of Nb ₂ O ₅ or Ta ₂ produced by anodizing the porous sintered body O is ₅ . The pores of the sintered body may be filled with a cathode material which is contacted with a cathode conductor.

For the cathode side Electrode of solid electrolytic capacitors are usually electrically conductive Polymers used. These become known through oxidation of a monomer by means of an oxidizing agent or electrochemically polymerized become. The properties of the finished solid electrolytic capacitor, For example, ESR, the aging behavior, the dielectric strength and the leakage current is hanging decisive from the type of monomer used. In general, a specific Property of the solid electrolyte capacitor be obtained with a polymer, which of a certain Monomer is derived. Other properties may help to optimize others Require monomers or polymers derived therefrom. So far but failed to find polymers simultaneously the requirements for high withstand voltage or a low Leakage current with low resistance values (ESR) or low impedances to combine. For this reason, with known electrically conductive polymers respectively only a compromise on the property profile of the capacitors reached.

Known electrically conductive Polymers for the Electrodes of solid electrolytic capacitors have been through Layerwise combination of similar or different polymers especially PEDT (poly-ethylenedioxythiophene), polypyrrole, Polyaniline and others. The polymers are made by electrochemical Polymerization of suitable monomers or by chemical polymerization by means of oxidizing agents, for example Fe (III), Cu (II), Ce (IV), Perchlorates, peroxides and others. This succeeds the Preparation of an electrically conductive polymer which is doped can be deposited or stabilized by suitable counterions can be.

For coating capacitors with these electrically conductive polymers, it is known to immerse the anode body first in a monomer solution and then in the solution of an oxidizing agent (see, for example, US Pat. US 66 14 063 B2 ). Alternatively, the anode body can also be impregnated with a mixture of monomer and oxidizing agent and then polymerized, see, for example DE 38 14 730 A1 , The polymerization processes are optionally repeated several times in order to achieve the desired layer thickness of conductive polymers and thus the desired conductivity.

With However, all these homopolymers have so far only capacitors are obtained with property profiles that are not in all respects are optimal.

From the DE 694 08 284 T2 For example, a solid electrolytic capacitor having an electrically conductive polymer coating as a cathode and an anode of valve metal is known in which the polymer coating comprises a polypyrrole or a copolymer of pyrrole and its derivatives or a copolymer of pyrrole and aniline.

From the EP 0 358 239 A2 For example, a conductive polymer cathode solid electrolytic capacitor is known in which the conductive polymer is polypyrrole or polythiophene produced by electrolytic polymerization.

task It is the object of the present invention to provide a suitable electrode layer electrically conductive Specify coating that in the property profile compared to the known homopolymeric is improved.

These The object is achieved by a with an electrically conductive Layering provided with the features ceramic body Claim 1 solved. Advantageous embodiments of the invention and a method for Preparation of the coating can be found in further claims.

A ceramic body according to the invention has a coating of a co-polymer based on at least two different monomers. These are selected from the known group of monomers used hitherto for homopolymers and include pyrrole, thiophene and derivatives thereof. Surprisingly, these co-polymers have a property profile on, in which the positive properties of the respective monomers combine, without at the same time their disadvantages must be included. A particularly advantageous co-polymer can be prepared from the monomers pyrrole and thiophene. Solid electrolyte capacitors coated in this way are distinguished from known capacitors by a lower leakage current and lower ESR values with simultaneously improved aging behavior, in particular when compared with the co-polymers of the respective pure monomers.

Advantageous is the ceramic body on the surface formed essentially of the oxide of a valve metal. On These dielectric layers, the co-polymers have a especially good adhesion. The oxides mentioned are, for example for the production of anode bodies for solid electrolyte capacitors used.

Is possible However, it also, the electrically conductive coating on any other dielectric ceramics, where they usually also a good adhesion with constant electrical properties exhibit. In the preferred application, the coating is applied a ceramic body whose ceramic surface consists essentially of tantalum or niobium oxide. These are the materials that are preferred in solid electrolyte capacitors with tantalum or niobium anode body be used. In these cases the invention is electrically conductive Coating of the mentioned co-polymers used as a cathode. A coating according to the invention has several sublayers of the same or different Composition on. While the thickness of each sub-layer results from the particular coating process used, will over the number of partial layers the desired conductivity or the desired one Total thickness of the coating set. A preferred conductivity is for example in the range of 80-120 mS / cm.

to Production of electrically conductive Coating on a ceramic body at least two different Monomers oxidatively crosslinked to form an electrically conductive co-polymer. The monomers are selected from pyrrole, thiophene and their derivatives.

The Oxidation can be done chemically, wherein also the oxidizing agent in liquid or dissolved form on the ceramic body can be applied. In this case, first the monomer or first the Oxidizing agent and then the respective reaction partners are applied to the body. The Oxidation itself can be carried out under suitable conditions, preferably at increased Temperature, performed become. Become solutions used, so can advantageously after each wetting process Evaporation of the solvent in air and / or at elevated temperatures Temperature and / or reduced pressure, then compared to a second wetting process is more stable, thus allowing a thicker Layer of the respective reagent to produce.

One preferred oxidizing agent for the monomers mentioned are oxidative salts of metal ions, for example, iron (III) salts. These may preferably be in aqueous or alcoholic solution be used.

The Application of liquid or solutes can be done in any application method, but with spray coating or diving the body into the appropriate solution or liquid are particularly suitable. If the ceramic body is an anode body of a Solid electrolyte capacitor, so the porous surface of the anode body is special well suited to absorb a sufficient amount of each solution and into the pores. The networking then finds in the superficial Pores instead, with a dense coating of the co-polymer arises.

As already mentioned, For example, the production of thicker electrically conductive coatings may involve multiple sublayers require. For this purpose, it is advantageous to have a first part-layer in the to produce said manner on the ceramic body and to polymerize. Subsequently the process steps are repeated, wherein a second sub-layer is generated, which firmly adheres to the first sub-layer. It is it is possible the process conditions in the production of the other sub-layers towards those to vary the first sub-layer and also partial layers with to produce the first partial layer deviating co-polymers or for generating the partial layers different mixtures of monomers to use. Another degree of freedom for fine-tuning the properties of the electrically conductive coating used can be, is the quantity ratio the monomers to be crosslinked in an oxidation process. The variation or combination of different monomers in different stoichiometries or molar ratios now allows the synthesis of tailored electrically conductive Copolymers which are the desired Combine properties of the respective monomers.

For the preparation of conductive polymers, the anodic oxidation of monomers can be used. In this process variant, a first partial layer is first produced by chemical polymerization of monomers. Subsequently This layer is connected to an anode and immersed in a solution of a corresponding monomer mixture. In this way, it is possible to increase the layer thickness of this first sub-layer continuously by anodic crosslinking, so that the method can be controlled particularly well. In this case, it is advantageous to control the polymerization rate via the fed-in stream.

in the The invention is based on embodiments and the associated figures explained in more detail. The Figures are only for a better understanding of the invention and are therefore only schematically and not to scale. Same Parts are designated by the same reference numerals.

1 shows two different methods for applying a monomer or oxidant-containing solution,

2 shows a ceramic body with a first conductive coating,

3 shows a ceramic body with a multilayer electrically conductive coating,

4 shows a solid state electrolytic capacitor with electrically conductive coating in the schematic cross section.

1a shows the coating of a ceramic body KK by means of spray coating, wherein for example by means of a nozzle, a corresponding droplet mist N of the ceramic body to KK applied solution is generated. During the coating, the ceramic body can be rotated accordingly, so that all wetted or coating surface areas can be wetted by the solution.

1b shows another possibility in which the ceramic body KK is immersed in a solution L introduced in a container B. Depending on the immersion depth, the surface to be wetted can be defined. In the situation shown, for example, an end region of the ceramic body KK remains unwetted by the solution L.

The dip coating according to 1b has the advantage that in this way a maximum amount of solution can be applied to the surface of the ceramic body KK. However, it is disadvantageous that two different solutions are generally required for carrying out a polymerization according to the invention, wherein during the second dipping process or when applying the second component, a part of the first component can be dispensed into the solution with the second component and contaminated thereby. Since in this way monomers come into contact with oxidizing agent, this can lead to undesirable precipitations in the solution with the monomers or with the oxidizing agent. It is therefore advantageous, for example, to apply the first component by means of dip coating and the second component by means of spraying.

After application of the two components, the ceramic body is exposed to a particular elevated temperature in order to initiate the polymerization. By crosslinking of the monomers, a conductive coating LB is formed on the ceramic body KK, as shown in FIG 2 is shown with reference to the schematic cross section.

By repeating the wetting and polymerization steps, it is possible to produce a multilayer conductive coating LB, as shown for example by a schematic cross-section in FIG 3 is shown. Although different partial layers are shown in the figure, the interface of the partial layers is usually no longer distinguishable from one another in the finished coated body because of their good mutual adhesion and chemical similarity. The ceramic body has here, for example, three electrically conductive partial layers LB1, LB2 and LB3.

in the The following are exemplary process instructions for the production a co-polymer of the invention on a ceramic body, here an anodized tantalum sintered body, indicated. The relative amounts are given in percent by weight.

First embodiment

One anodized Ta sintered body will be first immersed in a first solution containing a mixture of two monomers. The solution contains 0.5 to 5% of 3,4-ethylene-dioxythiophene, 0.5 to 5% of pyrrole, 10 to 30% sodium alkylnaphthylsulfone sulfonate and 5 to 25% isopropanol, the rest is water. Subsequently becomes the ceramic body in a watery solution immersed with oxidizing agent. This contains 10 to 25% Fe (III) sulfate, 0.5% sulfuric acid and water. Subsequently the polymerization is carried out at a temperature between -5 and 105 ° C.

Finally, a reforming and washing process is carried out in an aqueous-acidic solution containing, for example, toluenesulfonic acid, phosphoric acid and citric acid. In this way, a first sub-layer is generated. An electrically conductive coating with said Co-polymer suitable for the cathode of the tantalum solid electrolytic capacitor is obtained by repeating the process steps five to twelve times.

Second embodiment

One anodized tantalum sintered body 1 minute in a butanolic solution of 0.5 to 5% 3,4-ethylene-dioxythiophene, 0.5 to 5% pyrrole, 30% Fe (III) toluenesulfonate immersed.

Directly subsequently the polymerization of the monomers takes place by means of the common applied oxidizing agent, wherein a temperature between -5 ° and + 125 ° C set becomes. Finally Again, a reforming and washing process in aqueous-acidic solution as in the first embodiment. The process steps are repeated three to ten times to the desired Layer thickness of the pyrrole-EDT copolymer to produce.

Third embodiment

One anodized tantalum sintered body will be first in an ethanolic solution from 10 to 40% Fe (III) toluenesulfonate immersed and then at 15 up to 105 ° C dried. Then immersed in a monomer-containing solution, for example in a solution from 1 to 20% 3,4-ethylene-dioxythiophene and 1 to 20% pyrrole in Ethyl acetate. The subsequent polymerization takes place at -5 to + 125 ° C. Finally again a reforming washing process in watery-sour Solution. The cycle will be four to twelve Repeated times to the desired Layer thickness of pyrrole-EDT copolymer to produce.

Fourth embodiment

One anodized Ta sintered body is coated with a first sublayer of an EDT pyrrole copolymer according to a Process variant according to one of the embodiments 1 to 3 coated. Subsequently the thus coated ceramic body is in a solution of 0.5 to 5% 3,4-ethylenedioxythiophene, 0.5 to 5% of pyrrole, 10 to 30% Sodium Alkylnaphthylsulfonsulfonat, 5 to 25% isopropanol and water immersed. Subsequently, will the first co-polymer sublayer connected to an electrode and connected as an anode. This takes place an electrochemical anodic oxidation, wherein a layer of EDT pyrrole copolymer grows up. The procedure can be carried out without interruption until a sufficient layer thickness is reached.

The inventive method can be used to make electrically conductive coatings on any Types of ceramic bodies or ceramic surfaces be used. Therefore, the use in solid electrolyte capacitors is particularly preferred like tantalum or niobium capacitors as well as in aluminum polymer capacitors.

4 shows a tantalum solid electrolytic capacitor according to the invention provided with an electrically conductive cathode coating in the schematic cross section. The capacitor consists of an anode wire AD, around which a porous anode body AK made of pressed and sintered tantalum powder is applied. Anodic oxidation of the surface of the anode body produces a superficial oxide layer, which as a dielectric DE completely or partially surrounds the surface of the anode body. On the surface of the dielectric DE, the cathode is applied in the form of the conductive coating LB. By a suitable choice of the coating conditions, a short circuit between the conductive coating and the anode wire AD is prevented.

Claims (9)

Dielectric ceramic body or body with a dielectric ceramic surface, on which an electrically conductive coating is arranged is made up of several over each other arranged sub-layers of a copolymer consists, which on at least two different monomers of pyrrole and thiophene and their derivatives. body according to claim 1, wherein the partial layers have different composition exhibit. body according to claim 1 or 2, wherein the body is the dielectric of a Solid electrolytic capacitor represents and the electrically conductive coating represents the cathode terminal of the solid electrolytic capacitor. body according to claim 3, wherein the solid electrolytic capacitor with the electrically conductive Coating as cathode terminal has a tantalum or niobium anode body. A method for producing an electrically conductive coating on a dielectric ceramic body or a body with a dielectric ceramic surface, in which - either the body is first wetted with a solution containing a mixture of at least two different monomers selected from the group pyrrole, thiophene and their Contains derivatives, and the monomers are brought into contact with a solution of an oxidizing agent, or the order of treatment with the solutions is reversed, - the monomers to an electrically conductive Co be crosslinked polymer, - the steps of treatment are performed repeatedly alternating. A method according to claim 5, wherein as the oxidizing agent Iron (III) salts are used. Method according to one of claims 5 or 6, wherein the wetting with a solution by spraying with or immersion in the respective solution. Method according to one of claims 5 to 7, wherein the number the sublayers resulting from the alternating wetting so chosen that is an electrical conductivity the coating of 80-120 mS / cm. Method according to one of claims 5 to 8, - in which the body first with one compared to the desired one Layer thickness relatively thin Provided partial layer of an electrically conductive copolymer becomes, - at the body in a solution the at least two monomers are immersed - in which the sub-layer is connected to an anode, - and the Partial layer by anodic oxidation and polymerization of Monomers is amplified so long until a desired Layer thickness or a desired electric conductivity is reached.