Method for producing polymer capacitors for high reliability applications

Abstract

The invention relates to a method for producing a capacitor, comprising the following method steps: a) providing a porous electrode body (1) made of an electrode material (2) wherein a dielectric (3) at least partially covers the surface of said electrode material (2); b) introducing a liquid composition comprising an electrically conductive polymer and a dispersant into at least a portion of the porous electrode body (1) provided in method step a), wherein the electrically conductive layer made from the liquid composition has an electrical conductivity of less than 100 S / cm; c) at least partially removing the dispersant from the porous electrode body (1) obtained in method step b) to form a solid electrolyte layer (4) at least partially covering the surface of the dielectric (3); d) filling at least a portion of the pores (5) of the porous electrode body (1) obtained in method step c) with an impregnation solution comprising at least one impregnation solvent, wherein the at least one impregnation solvent has a boiling point of at least 150 DEG C (determined at 1013 hPa); e) encapsulating the porous electrode body (1) obtained in method step d); f) heating the encapsulated electrode body obtained in method step e) at a temperature above 50 DEG C for more than 10 minutes. The invention also relates to a capacitor produced by such a method, to the use of an electrolytic capacitor and to an electronic circuit.

Description

[0001] The present invention relates to a method for manufacturing a capacitor, a capacitor obtainable by this method, the use of such a capacitor, and an electronic circuit.

[0002] Standard electrolytic capacitors typically consist of a porous metal electrode, an oxide layer provided on the metal surface, a conductive material (usually solid) introduced into the porous structure, external electrodes (contacts) such as a silver layer, and other electrical contacts and encapsulations. A frequently used electrolytic capacitor is the tantalum electrolytic capacitor, the anode electrode of which is made of the valve metal tantalum, on which a uniform tantalum pentoxide dielectric layer has been produced by anodic oxidation (also known as "forming"). A liquid or solid electrolyte forms the cathode of the capacitor. Aluminum capacitors are also frequently used, the anode electrode of which is made of the valve metal aluminum, on which a uniform electrically insulating aluminum oxide layer has been produced as a dielectric by means of anodic oxidation. Here, in addition, a liquid electrolyte or a solid electrolyte forms the cathode of the capacitor. Aluminum capacitors are typically embodied as wound capacitors or stacked capacitors.

[0003] Due to their high electrical conductivity, π-conjugated polymers are particularly suitable as solid electrolytes in the above-mentioned capacitors. π-Conjugated polymers are also known as conducting polymers or synthetic metals. They are gaining increasing commercial significance because polymers have advantages in terms of processing, weight, and selective adjustment of properties by chemical modification compared to metals. Examples of known π-conjugated polymers include polypyrrole, polythiophene, polyaniline, polyacetylene, polyphenylene, and poly(phenylene-vinylene), where poly(3,4-ethylenedioxythiophene) (PEDOT) is a particularly important polythiophene used technically because it has a very high electrical conductivity in its oxidized form.

[0004] Therefore, in the prior art, alternative methods for manufacturing solid electrolytes based on conducting polymers in electrolytic capacitors have been developed. For example, DE-A-10 2005 043828 describes a method for manufacturing a solid electrolyte in a capacitor, in which a dispersion containing already polymerized thiophene (for example, a PEDOT / PSS dispersion known from the prior art) is applied to the oxide layer, and then the dispersion medium is removed by evaporation.

[0005] However, it has been observed that when used in an electronic circuit, the electrical properties of the capacitor deteriorate during its lifetime, especially due to the switching-on and switching-off processes in the electronic circuit or due to long-term exposure to high temperatures. This applies in particular to the capacitance of capacitors whose solid electrolyte layer is based on PEDOT / PSS.

[0006] The present invention is based on the following objectives: to overcome the disadvantages associated with capacitors, preferably with solid electrolytic capacitors, more preferably with capacitors known from the prior art that include a solid electrolyte layer based on a π-conjugated polymer such as PEDOT, and even more preferably with capacitors known from the prior art that include a solid electrolyte layer based on PEDOT / PSS.

[0007] In particular, the present invention is based on the following objective: to provide a method for manufacturing capacitors, by means of which such capacitors can be manufactured that, when used in electronic circuits, exhibit as constant electrical properties as possible, in particular a capacitance that varies as little as possible, over as long a period of time as possible.

[0008] Another objective of the present invention is to provide capacitors with a low equivalent series resistance (ESR) and high reliability, particularly with respect to capacitance at high temperatures.

[0009] A further feature of the manufacturing method for the above-mentioned advantageous capacitors should also be that it allows these capacitors to be manufactured in the simplest possible way, in particular with the fewest possible method steps.

[0010] The independent claims contribute to solving at least one, preferably more than one, of the above-mentioned objectives. The dependent claims provide preferred embodiments that contribute to solving at least one of the said objectives.

[0011] |1a| The contribution to solving at least one of the objectives according to the present invention is made by a first embodiment of a method for manufacturing capacitors, preferably electrolytic capacitors, which method comprises the following method steps:

[0012] a) Providing a porous electrode body made of electrode material, wherein a dielectric at least partially covers the surface of this electrode material;

[0013] b) Applying

[0014] i) A liquid composition A, preferably a dispersion A, which comprises a conductive polymer and a dispersant, wherein the conductive layer made of the liquid composition A has a conductivity of less than 100 S / cm, preferably less than 25 S / cm, more preferably less than 10 S / cm, even more preferably less than 4 S / cm, and most preferably less than 1 S / cm;

[0015] or

[0016] ii) A liquid composition B, preferably a dispersion B, which comprises a conductive polymer and a dispersant, wherein the liquid composition B comprises, in each case based on the total weight of the liquid composition B, less than 3% by weight, preferably less than 1% by weight, more preferably less than 0.5% by weight, even more preferably less than 0.1% by weight, and most preferably less than 0.01% by weight of a high-boiling solvent having a boiling point of at least 150 °C, preferably at least 170 °C and more preferably at least 185 °C (determined at 1013 hPa), and wherein it is particularly preferred that the liquid composition B is substantially free of, preferably free of, high-boiling solvents;

[0017] or

[0018] iii) A liquid composition C, preferably a dispersion C, which comprises a conductive polymer and a dispersant, wherein the liquid composition C comprises, in each case based on the total weight of the liquid composition C, less than 3% by weight, preferably less than 1% by weight, more preferably less than 0.5% by weight, even more preferably less than 0.1% by weight, and most preferably less than 0.01% by weight of a high-boiling solvent having a boiling point of at least 150 °C, preferably at least 170 °C and more preferably at least 185 °C (determined at 1013 hPa), and wherein the conductive layer made from the liquid composition C has a conductivity of less than 100 S / cm, preferably less than 25 S / cm, more preferably less than 10 S / cm, even more preferably less than 4 S / cm and most preferably less than 1 S / cm, and wherein it is particularly preferred that the liquid composition C is substantially free of, preferably free of, high-boiling solvents; introduced into at least a part of the porous electrode body provided in method step a);

[0019] c) At least partially removing the dispersant from the porous electrode body obtained in method step b) to form a solid electrolyte layer that at least partially covers the surface of the dielectric;

[0020] d) Filling at least a part of the pores of the porous electrode body obtained in method step c) with an impregnation solution comprising at least one impregnation solvent, wherein the boiling point (determined at 1013 hPa) of the at least one impregnation solvent is at least 150 °C, preferably at least 170 °C, and more preferably at least 190 °C;

[0021] e) Encapsulating the porous electrode body obtained in method step d), wherein preferably, before encapsulating the porous electrode body, less than 20% by weight, preferably less than 10% by weight and more preferably less than 1% by weight of the impregnation solution that has been used to fill a part of the pores of the porous electrode body in method step d) evaporates, and wherein even more preferably, before encapsulating the porous electrode body, substantially the entire amount, most preferably the entire amount of the impregnation solution that has been used to fill a part of the pores of the porous electrode body in method step d) remains in the porous electrode body;

[0022] f) Heating the encapsulated electrode body obtained in method step e) at a temperature above 50 °C, more preferably above 75 °C and even more preferably above 100 °C for more than 10 minutes, preferably more than 20 minutes and more preferably more than 30 minutes.

[0023] As used herein, the term "high-boiling solvent having a boiling point (determined at 1013 hPa) of at least 150 °C" preferably refers to a compound that actually boils (i.e., its aggregate state changes from liquid to gaseous) at a temperature of at least 150 °C. This term preferably does not include compounds that do not actually boil but decompose before boiling at high temperatures (such as polyethylene glycol 400).

[0024] The combination of method steps b) and c) can be carried out only once or can be repeated several times, such as 2 times, 3 times, 4 times, 5 times, 6 times, 7 times, 8 times, 9 times or at least 10 times.

[0025] According to the first and most preferred variant of the method according to the invention, in method step b), the liquid composition A, preferably the dispersion A, is introduced into at least a part of the porous electrode body provided in method step a). In this context, it is also preferred that the conductivity of the conductive layer made of the liquid composition A is not less than 0.1 S / cm, and preferably not less than 0.2 S / cm. Preferably, the conductive layer made of the liquid composition A has a conductivity in the range of 0.1 S / cm to less than 10 S / cm, even more preferably in the range of 0.1 S / cm to less than 4 S / cm and most preferably in the range of 0.1 S / cm to less than 1 S / cm)

[0026] According to the second variant of the method according to the invention, in method step b), the liquid composition B, preferably the dispersion B, is introduced into at least a part of the porous electrode body provided in method step a).

[0027] According to a third variant of the method according to the invention, in method step b), the liquid composition C, preferably the dispersion C, is introduced into at least a part of the porous electrode body provided in method step a). In this context, it is also preferred that the conductive layer made of the liquid composition C has a conductivity of not less than 0.1 S / cm and preferably not less than 0.2 S / cm. Preferably, the conductive layer made of the liquid composition C has a conductivity in the range of 0.1 S / cm to less than 10 S / cm, even more preferably in the range of 0.1 S / cm to less than 4 S / cm, and most preferably in the range of 0.1 S / cm to less than 1 S / cm)

[0028] The liquid compositions A, B or C used in method step b) may be in the form of a solution or a dispersion. However, the transformation here can be fluid. For this reason, no distinction is made hereinafter between the terms "dispersed" and "dissolved". Similarly, no distinction is made between "dispersion" and "solution" or between "dispersant" and "solvent". Instead, these terms are used synonymously hereinafter. However, the liquid compositions A, B or C preferably exist in the form of a dispersion in which the conductive polymer is dispersed in a dispersant.

[0029] |2a| According to a preferred embodiment of the method according to the invention, the electrode material is aluminum and the dielectric is alumina, preferably Al2O3. This preferred embodiment is the second embodiment of the method according to the invention, and this second embodiment preferably depends on the first embodiment.

[0030] |3a| According to another preferred embodiment of the method according to the invention, the liquid composition A, B or C used in method step b), preferably the liquid composition A, contains particles of a conductive polymer. In this context, it is particularly preferred that the diameter d of these particles 50 is preferably in the range of 1 nm to 100 nm, preferably in the range of 1 nm to less than 70 nm, preferably in the range of 1 nm to 50 nm, particularly preferably in the range of 1 nm to 40 nm, and even more particularly preferably in the range of 5 nm to 30 nm. The determination of the diameter of these particles is carried out via ultracentrifugation measurement. This preferred embodiment is the third embodiment of the method according to the invention, and this third embodiment preferably depends on the first embodiment or the second embodiment.

[0031] |4a| According to another preferred embodiment of the method according to the invention, the conductive polymer comprises at least one polymer selected from the group consisting of polythiophene, polypyrrole, polyaniline, and mixtures of at least two of them. This preferred embodiment is the fourth embodiment of the method according to the invention, and this fourth embodiment preferably depends on any one of the first to third embodiments.

[0032] |5a|According to another preferred embodiment of the method according to the invention, the conductive polymer is poly(3,4-ethylenedioxythiophene) or a derivative thereof. This preferred embodiment is the fifth embodiment of the method according to the invention, and this fifth embodiment preferably depends on any one of the first to fourth embodiments.

[0033] |6a|According to another preferred embodiment of the method according to the invention, the liquid composition A, B or C used in method step b), preferably liquid composition A, further comprises at least one polymeric anion. This preferred embodiment is the sixth embodiment of the method according to the invention, and this sixth embodiment preferably depends on any one of the first to fifth embodiments.

[0034] |7a|According to another preferred embodiment of the method according to the invention, the polymeric anion is polystyrene sulfonic acid or a derivative thereof. In this context, it is particularly preferred that the conductive polymer in the liquid composition A, B or C used in method step b), preferably liquid composition A

[0035] is present in the form of a polythiophene / (poly)anion complex, where the polythiophene is poly(3,4-ethylenedioxythiophene) and the polyanion is the anion of polystyrene sulfonic acid. This preferred embodiment is the seventh embodiment of the method according to the invention, and this seventh embodiment preferably depends on the sixth embodiment.

[0036] |8a|According to another preferred embodiment of the method according to the invention, in method step b)

[0037] the pH value (determined at 25 °C) of the liquid composition A, B or C used, preferably liquid composition A, is in the range from 2.5 to 8.0, preferably in the range from 2.5 to 7, and more preferably in the range from 3 to 6. This preferred embodiment is the eighth embodiment of the method according to the invention, and this eighth embodiment preferably depends on any one of the first to seventh embodiments.

[0038] |9a|According to another preferred embodiment of the method according to the invention, in method step d)

[0039] Fill at least 25% by volume, more preferably at least 30% by volume, even more preferably at least 40% by volume, even more preferably at least 50% by volume, even more preferably at least 75% by volume, and most preferably at least 90% by volume of the pore volume of the porous electrode body obtained in method step c) with the impregnation solution. This preferred embodiment is the ninth embodiment of the method according to the present invention, and this ninth embodiment preferably depends on any one of the first to eighth embodiments.

[0040] |10a| According to another preferred embodiment of the method according to the present invention, in method step d),

[0041] the ionic conductivity of the impregnation solution used is less than 1000 μS / cm, preferably less than

[0042] 100 μS / cm, even more preferably less than 10 μS / cm, and most preferably less than

[0043] 1 μS / cm. This preferred embodiment is the tenth embodiment of the method according to the present invention, and this tenth embodiment preferably depends on any one of the first to ninth embodiments.

[0044] |11a| According to another preferred embodiment of the method according to the present invention, in method step d),

[0045] the impregnation solution used contains a mixture of at least two impregnation solvents. This preferred embodiment is the eleventh embodiment of the method according to the present invention, and this eleventh embodiment preferably depends on any one of the first to tenth embodiments.

[0046] |12a| According to another preferred embodiment of the method according to the present invention, in method step d),

[0047] the impregnation solution used contains at least one impregnation solvent, and the amount of the at least one impregnation solvent is at least 50% by weight, preferably at least 75% by weight, even more preferably at least 90% by weight, and most preferably at least 95% by weight in each case based on the total weight of the impregnation solution. In the case of two or more impregnation solvents, these amounts represent the total amount of the impregnation solvents. This preferred embodiment is the twelfth embodiment of the method according to the present invention, and this twelfth embodiment preferably depends on any one of the first to eleventh embodiments.

[0048] |13a| According to another preferred embodiment of the method according to the present invention, in method step d),

[0049] The melting point of at least one impregnation solvent in the impregnation solution used is less than 15 °C, preferably less than 5 °C, and even more preferably less than -5 °C. This preferred embodiment is the thirteenth embodiment of the method according to the present invention, and this thirteenth embodiment preferably depends on any one of the first to twelfth embodiments.

[0050] |14a| According to another preferred embodiment of the method according to the present invention, in method step d),

[0051] at least one impregnation solvent in the impregnation solution used has a boiling point (determined at 1013 hPa) of at least 200 °C and less than 330 °C. This preferred embodiment is the fourteenth embodiment of the method according to the present invention, and this fourteenth embodiment preferably depends on any one of the first to thirteenth embodiments.

[0052] |15a| According to another preferred embodiment of the method according to the present invention, in method step d),

[0053] at least one impregnation solvent in the impregnation solution used contains at least one hydroxyl group and has a molecular weight in the range of 70 g / mol to 195 g / mol, preferably in the range of 70 g / mol to 180 g / mol

[0054] range. In this context, it is further preferred that at least one impregnation solvent in the impregnation solution used in method step d) is a compound containing two hydroxyl groups or a compound containing one hydroxyl group and one ether group, preferably an alkyl ether group. This preferred embodiment is the fifteenth embodiment of the method according to the present invention, and this fifteenth embodiment preferably depends on any one of the first to fourteenth embodiments.

[0055] |16a| According to another preferred embodiment of the method according to the present invention, in method step d),

[0056] at least one impregnation solvent in the impregnation solution used is a compound containing two hydroxyl groups or a compound containing one hydroxyl group and one ether group, preferably an alkyl ether group, and polyglycols having 2 to 4 repeating units are particularly preferred as the impregnation solvent. This preferred embodiment is the sixteenth embodiment of the method according to the present invention, and this sixteenth embodiment preferably depends on any one of the first to fifteenth embodiments.

[0057] |17a| According to another preferred embodiment of the method according to the present invention, in method step d),

[0058] At least one impregnation solvent in the impregnation solution used is selected from the group consisting of diethylene glycol, triethylene glycol, tetraethylene glycol, and mixtures of at least two of them, and diethylene glycol and triethylene glycol are particularly preferred. This preferred embodiment is the seventeenth embodiment of the method according to the present invention, and this seventeenth embodiment preferably depends on any one of the first to sixteenth embodiments.

[0059] |18a|According to another preferred embodiment of the method according to the present invention, the liquid composition A, B, or C (preferably liquid composition A) used in method step b), the impregnation solution used in method step d), or both, preferably the impregnation solution used in method step d) further contains a stabilizer. This preferred embodiment is the eighteenth embodiment of the method according to the present invention, and this eighteenth embodiment preferably depends on any one of the first to seventeenth embodiments. Preferred stabilizers are those compounds mentioned in WO 2012 / 041507 A1, and aromatic compounds containing at least two OH groups and another functional group having a heteroatom different from carbon are particularly preferred. Examples of suitable stabilizers are 3,4,5-trihydroxybenzoic acid and its derivatives, such as 3,4,5-trihydroxybenzoate (gallate). In addition, alkyl esters, alkenyl esters, cycloalkyl esters, cycloalkenyl esters, and aryl esters will be mentioned, each of which preferably has 1 to 15 C atoms in the aryl or alkyl group of the ester. Particularly preferred are gallic acid and gallic acid esterified with sugar, which are generally referred to as tannins or gallotannins (see Chemie, 10th Edition (1999), page 4391). Also suitable as stabilizers are the "hydroxy-group-containing aromatic compounds" mentioned in paragraph

[0049] of EP 1 798 259 A1, the "anti-oxidants" mentioned in paragraph

[0025] of EP 1 043 720 A1, and the "aromatic compounds exclusive of sulfogroups and containing at least two hydroxy groups" mentioned on pages 10 and 11 of WO 2008 / 055834 A1. In this context, it is also preferred to use one or more stabilizers in a concentration ranging from 0.1% by weight to 60% by weight, preferably from 1% by weight to 25% by weight, and particularly preferably from 2% by weight to 10% by weight, based on the total weight of the impregnation solution. If the liquid composition A, B, or C used in method step b), preferably liquid composition A, contains a stabilizer, it is preferably to use one or more stabilizers in a concentration ranging from 0.1% by weight to 20% by weight, preferably from 0.5% by weight to 10% by weight, and particularly preferably from 1% by weight to 5% by weight, based on the total weight of the liquid composition.

[0060] |19a| According to another preferred embodiment of the method according to the invention, the method does not include any such method step: before encapsulating the porous electrode body in method step e), removing at least a part of the impregnation solution containing at least one impregnation solvent that has been used to fill at least a part of the pores of the porous electrode body, the impregnation solvent having a boiling point of at least 150 °C, preferably at least 170 °C, and more preferably at least 190 °C (determined at 1013 hPa). This preferred embodiment is the nineteenth embodiment of the method according to the invention, and this nineteenth embodiment preferably depends on any one of the first embodiment to the eighteenth embodiment.

[0061] |1b| The contribution to solving at least one of the objects according to the invention is made by the first embodiment of the capacitor, which can be obtained preferably by the method according to the invention, preferably by the method according to any one of the first embodiment to the nineteenth embodiment.

[0062] |2b|According to another preferred embodiment of the capacitor 1 according to the invention, the capacitor has a rated voltage in the range from 1 V to 250 V, preferably in the range from 6 V to 100 V and more preferably in the range from 10 V to 63 V. This preferred embodiment is the second embodiment of the capacitor 1 according to the invention, which preferably depends on the first embodiment.

[0063] |1c|The contribution to solving at least one of the objects according to the invention is made by the use of the capacitor according to the first or second embodiment in an electronic circuit, for example as a smoothing capacitor ("filter capacitor") or a decoupling capacitor ("decoupling capacitor"). The electronic circuit can be, for example, in a computer (desktop computer, laptop, server); in computer peripherals (e.g., PC cards); in portable electronic devices (such as mobile phones, digital cameras, chargers or consumer electronics); in consumer electronics equipment, such as in CD / DVD players and computer-game consoles; in navigation systems; in telecommunications devices, for example in base stations for mobile communications; in household equipment; in medical technology, for example in medical technology for defibrillators; in power supplies, such as power supplies based on renewable energy; or in automotive electronics, for example in automotive electronics for hybrid or electric vehicles.

[0064] |1d|The contribution to solving at least one of the objects according to the invention is made by an electronic circuit comprising the capacitor according to the first or second embodiment.

[0065] Method step a)

[0066] In method step a) of the method according to the invention, a porous electrode body made of an electrode material is provided, wherein the dielectric at least partially covers the surface of this electrode material.

[0067] In principle, the porous electrode body can be manufactured by pressing and sintering a valve metal powder with a high surface area to form a porous electrode body. In this context, an electrical contact wire, preferably made of a valve metal (such as tantalum), is conventionally pressed into the porous electrode body. Then, the porous electrode body is coated with a dielectric, i.e., an oxide layer, for example by electrochemical oxidation. As an alternative, a metal film can be etched and coated with a dielectric by electrochemical oxidation in order to obtain an anode film with porous regions. In the case of a wound capacitor, the anode film with porous regions (which forms the electrode body) and the cathode film are separated by a separator and wound.

[0068] Within the scope of the present invention, metals whose oxide coatings do not allow current to flow uniformly in both directions are understood as valve metals. When a voltage is applied to the anode, the oxide layer of the valve metal blocks the current flow, while when a voltage is applied to the cathode, a considerable current appears, which can destroy the oxide layer. Valve metals include Be, Mg, Al, Ge, Si, Sn, Sb, Bi, Ti, Zr, Hf, V, Nb, Ta, and W, as well as alloys or compounds of at least one of these metals with other elements. The best-known representatives of valve metals are Al, Ta, and Nb. A combination of electrical properties equivalent to those of valve metals is those having metallic conductivity, which can be oxidized and whose oxide layers provide the above properties. For example, NbO shows metallic conductivity but is generally not regarded as a valve metal. However, the layer of oxidized NbO shows the typical properties of a valve metal oxide layer, such that NbO or an alloy or compound of NbO with other elements is a typical example of such compounds having electrical properties equivalent to those of valve metals. Electrode materials made of tantalum, aluminum, and such electrode materials based on niobium or niobium oxide are preferred. Aluminum is particularly preferred as an electrode material.

[0069] To manufacture a porous electrode body, which often has porous regions, the valve metal can be sintered, for example, in powder form to provide a substantially porous electrode body, or alternatively, a porous structure can be imprinted onto the metal body. The latter can be implemented, for example, by etching a film.

[0070] Hereinafter, for simplicity, a body having porous regions is also referred to as porous. For example, an electrode body having porous regions is also referred to as a porous electrode body. On the one hand, the porous body can be penetrated by a plurality of channels and thus be sponge-like. This is often the case if tantalum is used in the construction of a capacitor. On the other hand, the pores can only be present at the surface, and the region provided below the surface pores can be formed in a solid manner. This is often observed if aluminum is used in the capacitor construction.

[0071] Then, by applying a voltage, the porous electrode body manufactured in this way is oxidized, for example, in a suitable electrolyte, such as an aqueous solution of phosphoric acid or ammonium adipate, to form a dielectric. The magnitude of this formation voltage depends on the thickness of the oxide layer to be achieved or respectively the subsequent operating voltage of the capacitor. The preferred formation voltage is in the range of 1 V to 1000 V, particularly preferably in the range of 10 V to 200 V, more preferably in the range of 15 V to 100 V, and even more preferably in the range of 20 V to 50 V.

[0072] The porous electrode body used preferably has a porosity of 10% to 90%, preferably 30% to 80%, particularly preferably 50% to 80%, and an average pore diameter of 10 nm to 10,000 nm, preferably 50 nm to 5,000 nm, particularly preferably 100 nm to 3,000 nm.

[0073] According to a specific embodiment of the method according to the invention, the electrolytic capacitor to be manufactured is an aluminum wound capacitor. In this case, in method step a), a porous aluminum film is anodically formed as the electrode material, thereby forming an aluminum oxide coating as the dielectric. Then the aluminum film (anode film) thus obtained is provided with contact lines and wound with a further porous aluminum film (cathode film) also provided with contact lines, whereby the two films are separated from each other by one or more separator papers, which are based on, for example, cellulose or preferably synthetic paper. After winding, the anode body obtained in this way is fixed, for example, by means of an adhesive tape. The one or more separator papers can be carbonized by heating in an oven. This way of manufacturing the anode body of an aluminum wound capacitor is well known from the prior art and is described, for example, in US 7,497,879 B2.

[0074] Method steps b) and c)

[0075] In method step b) of the method according to the invention, the liquid composition A, B or C as described in connection with the first embodiment of the method according to the invention, preferably the liquid composition A (subsequently simply referred to as - liquid composition -), preferably in the form of a dispersion comprising a conductive polymer and a dispersant, is introduced into at least a part of the porous electrode body provided in method step a). Then in method step c), the dispersant is at least partly removed to form a solid electrolyte which at least partly covers the surface of the dielectric.

[0076] Using known methods, such as dipping, impregnating, pouring, dripping, injecting, spraying, spreading, brushing or printing (for example, inkjet printing, screen printing or pad printing), the liquid composition is introduced into the porous area. The introduction is preferably carried out by dipping the porous electrode body provided in method step a) into the liquid composition and thus impregnating it with the liquid composition. The dipping into or impregnating with the liquid composition is preferably carried out for a duration in the range of 1 second to 120 minutes, particularly preferably in the range of 10 seconds to 60 minutes and most preferably in the range of 30 seconds to 15 minutes. The introduction of the liquid composition into the anode body can be facilitated, for example, by increasing or decreasing the pressure, vibration, ultrasound or heat.

[0077] The introduction of the liquid composition into the porous electrode body can be carried out directly or using an adhesion promoter (e.g., silanes such as organofunctional silanes or their hydrolysis products, e.g., 3-glycidoxypropyltrialkoxysilane, 3-aminopropyltriethoxysilane, 3-mercaptopropyl-trimethoxysilane, 3-methacryloxypropyltrimethoxysilane, vinyltrimethoxysilane or octyltriethoxysilane), and / or one or more other functional layers.

[0078] By means of this introduction, it is preferably achieved that the liquid composition has a lesser tendency to cover the pores of the porous region in layers. Instead, the surfaces of the cavities of the pores are at least partially coated with the liquid composition. In this way, the particles present in the liquid composition not only form a layer covering the openings of the pores; at least partially, all regions of the surface of the pores tend to be covered by a layer of particles of the liquid composition.

[0079] The term "polymer", as used within the scope of the present invention, includes all compounds having more than one identical or different repeating units within the meaning of the present invention.

[0080] The term "conductive polymer" here particularly refers to a class of compounds of π-conjugated polymers which have electrical conductivity after oxidation or reduction.

[0081] The conductive polymer in the liquid composition is preferably selected from the group consisting of optionally substituted polythiophenes, polypyrroles and polyanilines.

[0082] Particularly preferably, the conductive polymer comprises a polythiophene having repeating units selected from the group consisting of general formula (I), general formula (II) or general formula (III), or a combination of at least two of them. In the following possible variants, the conductive polymer in the dispersion comprises at least one polythiophene having a repeating unit of general formula (I) or general formula (II) or general formula (III), or repeating units of formula (I) and (II), or repeating units of formula (I) and (III), or repeating units of formula (II) and (III), or repeating units of formula (I), (II) and (III),

[0083]

[0084] where

[0085] A represents an optionally substituted C1-C5-alkylene residue,

[0086] R represents a straight-chain or branched-chain optionally substituted C1-C 18 -alkyl residue, an optionally substituted C5-C 12 -cycloalkyl residue, an optionally substituted C6-C 14-aryl residue, optionally substituted C7-C 18 -aralkyl residue, optionally substituted C1-C4-hydroxyalkyl residue or hydroxy residue,

[0087] x represents an integer from 0 to 8, and in the case where several residues R are bonded to A, these may be the same or different.

[0088] The general formulas (I) and (II) are to be understood such that the x substituents R may be bonded to the alkylene residue.

[0089] Polythiophenes having repeating units of general formula (I) or (II) or repeating units of general formulas (I) and (II) are particularly preferred, wherein A represents an optionally substituted C2-C3-alkylene residue and x represents 0 or 1. Optionally substituted poly(3,4-ethylenedioxythiophene) as a conductive polymer for solid electrolytes is highly particularly preferred.

[0090] Within the framework of the present invention, the prefix poly- is to be understood as meaning that the polymer or polythiophene contains more than one identical or different repeating unit. The polythiophene contains a total of n repeating units of general formula (I), or general formula (II), or general formula (III), or general formulas (I) and (II), or general formulas (I) and (III), or general formulas (II) and (III), or general formulas (I), (II) and (III), where n is an integer from 2 to 2000, preferably from 2 to 100. The repeating units of general formula (I) or general formula (II) or general formula (III), or the repeating units of general formulas (I) and (II), or the repeating units of general formulas (I) and (III), or the repeating units of general formulas (II) and (III), or the repeating units of general formulas (I), (II) and (III) may in each case be identical or different within one polythiophene. Polythiophenes having respectively identical repeating units of general formula (I) or general formula (II) or general formula (III), or having respectively identical repeating units of general formulas (I) and (II), or general formulas (I) and (III), or general formulas (II) and (III), or having respectively identical repeating units of general formulas (I), (II) and (III) are preferred. Polythiophenes having respectively identical repeating units of general formula (I) or general formula (II), or having respectively identical repeating units of general formulas (I) and (II) are particularly preferred.

[0091] The polythiophene preferably carries H at each end group.

[0092] Within the scope of the present invention, the C1-C5-alkylene residue A is preferably methylene, ethylene, n-propylene, n-butylene or n-pentylene. C1-C 18 -alkyl residue R preferably represents a straight-chain or branched C1-C 18- Alkyl residues such as methyl, ethyl, n-propyl or isopropyl, n-butyl, isobutyl, sec-butyl 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-C 12 - Cycloalkyl residue R represents, for example, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl or cyclodecyl, C5-C 14 - Aryl residue R represents, for example, phenyl or naphthyl, and C7-C 18 - Arylalkyl residue R represents, for example, benzyl, o-tolyl, m-tolyl, p-tolyl, 2,3-xylyl, 2,4-xylyl, 2,5-xylyl, 2,6-xylyl, 3,4-xylyl, 3,5-xylyl or mesityl. The above list is provided for the purpose of exemplarily explaining the present invention and should not be considered exclusive.

[0093] As optional further substituents of residue A and / or residue R, many organic groups are contemplated within the scope of the present invention, such as alkyl-, cycloalkyl-, aryl-, arylalkyl-, alkoxy-, halogen-, ether-, thioether-, disulfide-, sulfoxide-, sulfonate-, amino-, aldehyde-, ketone-, carboxylate-, carboxylic acid-, carbonate-, carboxylate-, cyano-, alkylsilane- and alkoxysilyl groups and carboxamide groups.

[0094] For example, the residues A and R listed above and / or the further substituents of residues A and R are contemplated as substituents of polyaniline or polypyrrole. Unsubstituted polyaniline is preferred.

[0095] The scope of the present invention includes all general residue definitions, parameters and explanations presented above and listed below or named within the preferred ranges, which general residue definitions, parameters and explanations are combined with each other, that is to say, any combination between the corresponding ranges and the preferred ranges.

[0096] The polythiophenes used as solid electrolytes in the preferred method can be neutral or cationic. In a preferred embodiment, they are cationic, where "cationic" only relates to the charge provided on the main polythiophene chain. Depending on the substituents on the residues, the polythiophenes can carry positive and negative charges within the structural unit, whereby the positive charge is set on the polythiophene main chain and the negative charge is optionally located on the residue R substituted by a sulfonate or carboxylate group. Thus, the positive charge on the polythiophene main chain can be partially or fully compensated by the anionic groups optionally present on the residue R. Generally, in these cases, the polythiophenes can be cationic, neutral or even anionic. However, within the scope of the present invention, they are all regarded as cationic polythiophenes because the positive charge on the main polythiophene chain is of decisive importance. The positive charge is not shown in the formula because its exact number and position cannot be accurately determined. However, the number of positive charges is at least 1 and at most n, where n represents the total number of all repeating units (identical or different) within the polythiophene.

[0097] For the compensation of the positive charge, assuming this has not occurred through the residue R optionally substituted with sulfonate or carboxylate and thus negatively charged, the cationic polythiophene requires an anion as a counterion.

[0098] The counterion can be a monomeric or polymeric anion, the latter also being referred to hereinafter as a polyanion. Compared with monomeric anions, polymeric anions are preferred because they contribute to the formation of the membrane and, due to their size, result in a more thermally stable conductive membrane.

[0099] The polymeric anions here can be, for example, the anions of polymeric carboxylic acids (such as polyacrylic acid, polymethacrylic acid or polymaleic acid) or polymeric sulfonic acids (such as polystyrene sulfonic acid and polyvinyl sulfonic acid). These polycarboxylic acids and polysulfonic acids can also be copolymers of ethylenically carboxylic acids and ethylenically sulfonic acids with other polymerizable monomers (such as acrylates and styrene).

[0100] The anions of the polycarboxylic acid or polysulfonic acid in the said particles are preferred as polymeric anions.

[0101] When using polythiophene, especially poly(3,4-ethylenedioxythiophene), it is particularly preferred to use the anion of polystyrene sulfonic acid (PSS) complexed in the form of the PEDOT / PSS complex known from the prior art as the polymeric anion. Such a complex can be obtained by the oxidative polymerization of thiophene monomers, preferably 3,4-ethylenedioxythiophene, in an aqueous solution in the presence of polystyrene sulfonic acid.

[0102] The molecular weight of the polyacid providing the polyanion is preferably from 1,000 to 2,000,000, particularly preferably from 2,000 to 500,000. The polybasic acid or its basic salts are commercially available, such as polystyrenesulfonic acid and polyacrylic acid, but can also be manufactured by known methods (see, for example, Houben Weyl, Methoden der organischen Chemie, Volume 20, Makromolekulare Stoffe, Part 2, (1987), [Methodsof Organic Chemistry,Macromolecular Substances], page 1141 et seq., etc.).

[0103] The polymeric anion and the conductive polymer can be included in the liquid composition, in particular in the dispersion in a weight ratio of 0.5:1 to 50:1, preferably 1:1 to 30:1, particularly preferably 1.5:1 to 20:1. In this context, assuming complete conversion during polymerization, the weight of the conductive polymer corresponds to the weighed amount of the monomers used.

[0104] As the monomer anion, those monomer anions of C1-C 20 -alkylsulfonic acids can be used, such as methane-, ethane-, propane-, butane- or higher sulfonic acids (such as dodecanesulfonic acid), aliphatic perfluorosulfonic acids (such as trifluoromethanesulfonic acid, perfluorobutanesulfonic acid or perfluorooctanesulfonic acid), aliphatic C1-C 20 -carboxylic acids (such as 2-ethylhexylcarboxylic acid), aliphatic perfluorocarboxylic acids (such as trifluoroacetic acid or perfluorooctanoic acid), and aromatic sulfonic acids (such as benzenesulfonic acid, o-toluenesulfonic acid, p-toluenesulfonic acid or dodecylbenzenesulfonic acid) and cycloalkanesulfonic acids (such as camphorsulfonic acid) optionally substituted by C1-C 20 -alkyl groups or tetrafluoroborates, hexafluorophosphates, perchlorates, hexafluoroantimonates, hexafluoroarsenates or hexachloroantimonates. The anions of p-toluenesulfonic acid, methanesulfonic acid or camphorsulfonic acid are preferred as the monomer anion.

[0105] Cationic polythiophenes containing anions as charge-compensating counterions are generally referred to in the art as polythiophene / (poly)anion complexes.

[0106] Also suitable as polythiophenes that can be used to form the solid electrolyte layer in method steps b) and c) are self-doped polythiophenes, which preferably contain at least 50%, still more preferably at least 75%, still more preferably at least 95%, and most preferably 100% of the repeating units of formula (I)

[0107]

[0108] wherein

[0109] X and Y are the same or different and represent O, S, N-R 1 , where R 1 represents aryl, C1-C 18 -alkyl or hydrogen,

[0110] Z represents an organic residue carrying at least one anionic substituent, preferably -SO3 - M + group, where M + represents a cation.

[0111] Preferred embodiments of the repeating unit according to formula (I)

[0112] Z represents -(CH2) m -CR 2 R 3 -(CH2) n -,

[0113] wherein

[0114] R 2 represents hydrogen, -(CH2) s -O-(CR 4 2) p -SO3 - M + or -(CH2) p -SO3 - M + ,

[0115] R 3 represents -(CH2) s -O-(CR 4 2) p -SO3 - M + or -(CH2) p -SO3 - M + ,

[0116] m and n are the same or different and represent integers from 0 to 3,

[0117] R 4 represents hydrogen or a C1-C 10 alkyl group, preferably a methyl group,

[0118] s represents an integer from 0 to 10, and

[0119] p represents an integer from 1 to 18,

[0120] and wherein R in the above formula 1 、R 2 、R 3 and R 4 may be the same or different.

[0121] In this context, the above percentage numbers are intended to represent the numerical content of the units of the structural formula (I) in the total number of monomer units in the self-doped conductive polymer.

[0122] Suitable cations M + are, for example, H + 、Li + 、Na + 、K + 、Rb + 、Cs + and NH4 + . Particularly suitable cations are Na + and K + .

[0123] Particularly preferred monomers of the structural formula (I) are monomers in which

[0124] X, Y represent O,

[0125] Z represents -(CH2) m -CR 2 R 3 -(CH2) n -,

[0126] R 2 represents hydrogen or -(CH2) s -O-(CH2) p -SO3 - M + 、-(CH2) p -SO3 - M + or -(CH2) s -O-

[0127] (CH2) p -CHR 4 -SO3 - M + ,

[0128] R 3 represents -(CH2) s -O-(CH2) p -SO3 - M + 、-(CH2) p -SO3 - M + or -(CH2)s -O-

[0129] (CH2) p -CHR 4 -SO3 - M + ,

[0130] M + represents a cation,

[0131] m and n are the same or different and represent an integer from 0 to 3,

[0132] R 4 represents hydrogen, a methyl group or an ethyl group;

[0133] s represents an integer from 0 to 10, and

[0134] p represents an integer of 1 to 18.

[0135] Very particularly preferred monomers of the formula (I) are monomers in which

[0136] X, Y represents O,

[0137] Z represents -(CH2)-CR 2 R 3 -(CH2) n -,

[0138] R 2 represents hydrogen,

[0139] R 3 Represents -(CH2) s -O-(CH2) p -SO3 - M + 、-(CH2) p -SO3 - M + 、-(CH2) s -O-

[0140] (CH2) p -CH(CH3)-SO3 - M + or -(CH2) s -O-(CH2) p -CH(CH2CH3)-SO3 - M + ,

[0141] M + Indicates Na + or K + ,

[0142] n represents 0 or 1,

[0143] s represents 0 or 1, and

[0144] p represents 2, 3, 4 or 5.

[0145] Suitable examples of self-doping polymers that can also be used to form the solid electrolyte layer in method steps b) and c) are disclosed in WO-A-2014 / 048562 and US-A-2015 / 0337061. Specific examples of very particularly preferred self-doping conductive polymers include poly(4-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]propane-1-sulfonic acid), poly(4-[(2,3-dihydrothieno[3,4-b][1,4]dioxin-2-yl)methoxy]butane-1-sulfonic acid) (PEDOT-S), poly(4-[(2,3-dihydrothieno[3,4-b][1,4]dioxin-2-yl)methoxy]butane-2-sulfonic acid) or mixtures thereof.

[0146] Preferably, the conductive polymer in the liquid composition used in method step b) is present in particulate form, particularly preferably in the form of swollen gel particles of a polythiophene / (poly)-anion complex such as PEDOT / PSS. The specific conductivity of the particles is preferably less than 100 S / cm. In this context, the specific conductivity of the particles is the specific conductivity of a film in the dry state, which is formed from the particles upon drying of the dispersion. Preferably, a liquid composition is used, the particles of which have a specific conductivity of less than 25 S / cm, more preferably less than 10 S / cm, even more preferably less than 4 S / cm and most preferably less than 1 S / cm. In this context, it is also preferred that the particles have a specific conductivity of not less than 0.1 S / cm and preferably not less than 0.2 S / cm. Most preferably, the particles have a specific conductivity in the range from 1 S / cm to less than 10 S / cm, even more preferably in the range from 0.1 S / cm to less than 4 S / cm and most preferably in the range from 0.1 S / cm to less than 1 S / cm.

[0147] If the conductive polymer in the liquid composition used in method step b) is present in particulate form, then the diameter d of these particles 50 is preferably in the range from 1 nm to 100 nm, preferably in the range from 1 nm to less than 70 nm, preferably in the range from 1 nm to 50 nm, particularly preferably in the range from 1 nm to 40 nm, and more particularly preferably in the range from 5 nm to 30 nm. The determination of the diameter of these particles is carried out via ultracentrifugation measurements. Furthermore, it is preferred that the d of the particle size distribution of the conductive polymer in the liquid composition 90The value is less than 150 nm, particularly preferably less than 100 nm, and even more particularly preferably less than 50 nm. Furthermore, the d of the particle size distribution of the conductive polymer in the liquid composition 10 value is preferably greater than 1 nm, particularly preferably greater than 3 nm, and even more particularly preferably greater than 5 nm.

[0148] The liquid composition used in method step b) preferably comprises the purity of metals and transition metals as described in the document disclosed on pages 6, lines 10 - 29 of WO 2010 / 003874 A2. The main advantage of the low concentration of metals in the liquid composition is that the dielectric is not damaged during the formation of the solid electrolyte and during the subsequent operation of the capacitor.

[0149] The liquid composition used in method step b) further comprises at least one dispersant, and water, an organic solvent or a mixture of an organic solvent and water is preferred as the dispersant.

[0150] The following solvents can be named as examples of dispersants: aliphatic alcohols such as methanol, ethanol, isopropanol 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 carboxylic acid amides such as N - methylacetamide, dimethylacetamide and dimethylformamide; aliphatic and araliphatic ethers such as diethyl ether and anisole. In addition, water or a mixture of water and the above - mentioned organic solvents can also be used as a dispersant.

[0151] Preferred dispersants are water or other protic solvents such as alcohols, for example methanol, ethanol, isopropanol and butanol, and mixtures of water and these alcohols. Particularly preferred dispersant is water.

[0152] In addition, the liquid composition used in method step b) may contain further components, such as surface-active substances, for example ionic and non-ionic surfactants; or adhesion promoters, such as organofunctional silanes or their hydrolysis products, for example 3-glycidoxypropyl-trimethoxysilane, 3-aminopropyl-triethoxysilane, 3-mercaptopropyl-trimethoxysilane, 3-methacryloxypropyl-trimethoxysilane, vinyltrimethoxysilane or octyltriethoxysilane; crosslinking agents, such as melamine compounds, blocked isocyanates, functional silanes - for example, tetraethoxysilane, alkoxysilane hydrolysis products (for example alkoxysilane hydrolysis products based on tetraethoxysilane), epoxy silanes (such as 3-glycidoxypropyltrimethoxysilane-polyurethane), polyacrylates or polyolefin dispersions. The liquid composition used in method step b) may also contain one or more organic binders soluble in organic solvents, as described on page 12, lines 16 - 34 in WO 2009 / 141209 A1. The pH value of the liquid composition may be from 1 to 14, with a pH value from 1 to 8 being preferred. For corrosion-sensitive dielectrics such as alumina or niobium oxide, a liquid composition with a pH value from 2.5 to 8 is preferred to avoid damaging the dielectric, 2.5 to 7 is more preferred, and 3 to 6 is most preferred.

[0153] To adjust the pH value, for example, the bases or acids described on page 4, lines 13 - 32 in WO 2010 / 003874 A2 can be added to the liquid composition. Additives such as the base 2-dimethylaminoethanol, 2,2'-iminodiethanol or 2,2',2”-nitrilotriethanol and the acid polystyrenesulfonic acid, which do not impair the film formation of the liquid composition and do not volatilize at relatively high temperatures (for example at the soldering temperature), but remain within the solid electrolyte under these conditions, are preferred.

[0154] The viscosity of the liquid composition used in method step b) can depend on the application method and can be between 0.1 mPa×s and 1000 mPa×s (measured with a rheometer at 20 °C and a shear rate of 100 s -1 ). Preferably, the viscosity is from 1 mPa×s to 200 mPa×s, particularly preferably between 10 mPa×s and 150 mPa×s, and even more particularly preferably from 10 mPa×s to 100 mPa×s.

[0155] The solids content of the liquid composition used in method step b) is preferably in the range from 1 wt% to 30 wt%, particularly preferably in the range from 1 wt% to 20 wt%, and most particularly preferably in the range from 1 wt% to 10 wt%, in each case based on the total weight of the liquid composition. The solids content is determined by drying the dispersion at a temperature high enough to remove the dispersant, but not high enough to damage the solid material.

[0156] After the porous electrode body has been impregnated with the above liquid composition, the dispersant is at least partially removed in method step c) such that a solid electrolyte layer is formed which at least partially or completely covers the dielectric. In this context, it is preferred that the coverage of the dielectric by the solid electrolyte layer preferably amounts to at least 50%, particularly preferably at least 70%, and most preferably at least 80% of the amount, wherein the measurement of the capacitance of the capacitor at 120 °C under dry and humid conditions allows the determination as described in DE-A-10 2005 043 828.

[0157] The removal of the dispersant is preferably effected by removing the porous electrode body from the liquid composition used in method step b) and subsequently drying it, wherein the drying is preferably carried out at a temperature in the range from 20 °C to 200 °C, particularly preferably in the range from 50 °C to 180 °C, and more preferably in the range from 80 °C to 150 °C. The drying conditions (i.e. drying time, drying pressure and drying temperature) are preferably adjusted to ensure that at least 50% by weight, more preferably at least 75% by weight, even more preferably at least 90% by weight, even more preferably at least 95% by weight, and most preferably at least 99% by weight of the total amount of the dispersant is removed when forming the solid electrolyte layer. In a particularly preferred embodiment of the method according to the invention, the drying conditions are adjusted to ensure that the dispersant is completely removed when forming the solid electrolyte.

[0158] Method step d)

[0159] In method step d) of the method according to the invention, at least a part of the pores of the porous electrode body obtained in method step c) (i.e. the porous electrode body in which the dielectric is at least partially covered with a solid electrolyte layer) is filled with an impregnation solution comprising at least one impregnation solvent.

[0160] The immersion in the impregnation solution or the impregnation with the impregnation solution separately is preferably carried out for a duration in the range from 1 second to 120 minutes, particularly preferably in the range from 10 seconds to 60 minutes, and most preferably in the range from 30 seconds to 15 minutes. The immersion is preferably effected by immersing at least partially the porous electrode body obtained in method step c) in the impregnation solution or by injecting the impregnation solution into the porous electrode body and accordingly impregnating it with this impregnation solution. The introduction of the impregnation solution into the porous electrode body can be promoted, for example, by increasing or reducing the pressure, vibration, ultrasound or heat.

[0161] When impregnating the pores of the porous electrode body with the impregnation solution in method step d), it is preferred to ensure that the impregnation is achieved to such an extent that at least 50% by volume, more preferably at least 75% by volume, and even more preferably at least 90% by volume of the open pore volume of the porous electrode body obtained in method step c) is filled with the impregnation solution, wherein the impregnation solution preferably contains at least one impregnating solvent, and the amount of the at least one impregnating solvent is at least 50% by weight, preferably at least 75% by weight, even more preferably at least 90% by weight, and most preferably at least 95% by weight, in each case based on the total weight of the impregnation solution. In method step d), it is particularly preferred that these filling amounts are reached immediately before performing method step e), i.e., immediately before encapsulating the porous electrode body, to prevent further evaporation of the impregnating solvent from the pores. Thus, before encapsulating the porous electrode body, the impregnation solution applied in method step d) remains at least to some extent, preferably completely, within the pores of the porous electrode body.

[0162] The preferred impregnating solvents used in the method according to the invention satisfy at least one of the following properties, and more preferably they satisfy two of these properties:

[0163] (β1) Its boiling point (determined at 1013 hPa) is at least 200 °C and less than 330 °C;

[0164] (β2) Its melting point is less than 15 °C, preferably less than 5 °C, and even more preferably less than -5 °C.

[0165] In this context, it is particularly preferred that the at least one impregnating solvent is a compound containing two hydroxyl groups or a compound containing one hydroxyl group and one ether group, preferably an alkyl ether group. More preferably, the at least one impregnating solvent is a mono-, di-, tri- or tetraalkylene glycol, preferably diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol or tripropylene glycol, a mono-, di- or trialkylene glycol monoether, preferably diethylene glycol monomethyl ether, diethylene glycol monoethyl ether or diethylene glycol monobutyl ether, an alkanediol or an alkanediol monoether.

[0166] Preferred alkanediols are selected from the group consisting of: 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 1,5-pentanediol, 2,3-pentanediol, 2,4-pentanediol, 2-methyl-2,4-pentanediol, 1,2-hexanediol, 1,3-hexanediol, 1,4-hexanediol, 1,5-hexanediol, 1,6-hexanediol, 2,3-hexanediol, 2,4-hexanediol, 2,5-hexanediol, 3,4-hexanediol, 1,2-heptanediol, 1,3-heptanediol, 1,4-heptanediol, 1,5-heptanediol, 1,6-heptanediol, 1,7-heptanediol, 2,3-heptanediol, 2,4-heptanediol, 2,5-heptanediol, 2,6-heptanediol, 3,4-heptanediol, 3,5-heptanediol, 1,2-octanediol, 1,3-octanediol, 1,4-octanediol, 1,5-octanediol, 1,6-octanediol, 1,7-octanediol, 1,8-octanediol, 2,3-octanediol, 2,4-octanediol, 2,5-octanediol, 2,6-octanediol, 2,7-octanediol, 3,4-octanediol, 3,5-octanediol, 3,6-octanediol, 4,5-octanediol, and any other alkanediol having a molecular weight in the range of 70 g / mol to 180 g / mol. In addition, suitable as an impregnation solvent are derivatives of the above alkanediols, in which one hydrogen atom bonded to a carbon atom is replaced by an alkyl group, such as a methyl group or an ethyl group.

[0167] Particularly preferred are polyglycols having 2 to 4 repeating units. More preferably, the at least one impregnation solvent is selected from the group consisting of diethylene glycol, triethylene glycol, tetraethylene glycol, and mixtures of at least two of them, with diethylene glycol and triethylene glycol being most preferred.

[0168] In addition to the impregnation solvent, the impregnation solution may further contain additional components, such as stabilizers (such as those mentioned previously) and / or additional solvents, particularly low-boiling solvents having a boiling point (determined at 1013 hPa) less than 150 °C, preferably less than 120 °C. However, it is preferred that the impregnation solution used in method step d) contains at least one impregnation solvent, the amount of which is at least 50% by weight, preferably at least 75% by weight, and even more preferably at least 90% by weight, in each case based on the total weight of the impregnation solution. In the case of two or more impregnation solvents, these amounts represent the total amount of the impregnation solvents.

[0169] Encapsulation in method step e)

[0170] After at least a part of the pores of the porous electrode body obtained in method step c) has been filled with the impregnation solution in method step d), the electrolytic capacitor can be completed, in particular encapsulated, in a manner known to those skilled in the art. In this context, it is preferred that, before encapsulating the porous electrode body, less than 20% by weight, preferably less than 10% by weight and more preferably less than 1% by weight of the impregnation solution which has been used in method step d) to fill a part of the pores of the porous electrode body evaporates, and it is even more preferred that, before encapsulating the porous electrode body, substantially the entire amount, most preferably the entire amount, of the impregnation solution which has been used in method step d) to fill a part of the pores of the porous electrode body remains in the porous electrode body.

[0171] In the case of tantalum electrolytic capacitors, the capacitor body can be coated, for example, with a graphite layer and a silver layer as known from DE-A-10 2005043 828, while in the case of aluminum wound capacitors corresponding to the teaching of US 7,497,879 B2, the capacitor body is built into an aluminum cup which is provided with a sealing rubber and is mechanically firmly closed by flanging.

[0172] The encapsulation is preferably achieved by sealing the capacitor body with a resin (such as an epoxy resin or a thermoplastic resin, such as those disclosed in EP 0 447165A2). In the case of aluminum electrolytic capacitors, the encapsulation is preferably achieved by providing an aluminum cup for the porous electrode body obtained in method step e) and closing the aluminum cup with a sealing rubber.

[0173] Heat treatment in method step f)

[0174] In method step f), the encapsulated electrode body obtained in method step e) is heated at a temperature above 50 °C, more preferably above 75 °C and even more preferably above 100 °C for more than 10 minutes, preferably more than 20 minutes and more preferably more than 30 minutes. In this context, it is also preferred that the treatment temperature does not exceed 300 °C and the duration of the heat treatment does not exceed 24 hours, preferably does not exceed 3 hours and most preferably does not exceed 1 hour. Generally, the encapsulated capacitor is heated at a temperature of 100 °C to 200 °C for 10 minutes to 60 minutes.

[0175] The invention will now be explained in more detail with reference to the non-limiting drawings and examples.

[0176] Figure 1Shows a schematic cross-sectional view through a part of a capacitor obtained by the method according to the invention. The capacitor comprises a porous electrode body 1, which comprises pores 5 and is mainly made of a porous electrode material 2 such as aluminum. On the surface of the electrode material 2, a dielectric 3 is formed as a thin layer such that an anodic body which is still porous is formed, which anodic body comprises the electrode body 1 made of the electrode material 2 and the dielectric 3. On the dielectric 3, optionally after other layers, there follows a layer of a solid electrolyte 4 (e.g., made of PEDOT / PSS particles) such that a capacitor body is formed, which capacitor body comprises the electrode body 1 made of the electrode material 2, the dielectric 3 and the solid electrolyte 4. The pores 5 of the porous electrode body 1 are at least partially filled with an impregnating solution (e.g., diethylene glycol, triethylene glycol, tetraethylene glycol or a mixture of at least two of them; see Figure 1 the grey shading in

[0177] Figure 2 Shows an aluminum capacitor according to the invention, which aluminum capacitor comprises a capacitor element 8 (a porous electrode material 2 coated with a dielectric 3 and a solid electrolyte 4) and leads 10, which leads contact a porous anode foil and an opposite cathode foil, the two foils being wound with separator paper between them and fixed with a winding end strip. The capacitor element 8 is held in an aluminum housing 7 in the shape of a cylinder with a bottom, and a rubber sealant 9 is attached in the opening of the housing.

[0178] Measurement method :

[0179] Solid content

[0180] To determine the solids content, 5 g of the liquid composition used in method step b) is dried at 100 °C for 15 h and the solids content is determined by weighing the difference in weight.

[0181] pH value

[0182] The pH value is determined with a pH meter. After calibration, the pH electrode is placed into the slowly stirred dispersion or solution until the reading of the pH is constant.

[0183] Conductivity

[0184] Place a clean glass substrate on a spin coater and distribute 10 ml of the liquid composition used in method step b) over the substrate. Then spin out the remaining solution by rotating the plate. Then, dry the so-coated substrate on a hot plate at 130 °C for 15 minutes. Then determine the layer thickness d with the aid of a layer thickness measuring device (Tencor, Alphastep 500). Determine the conductivity by vapor deposition of a 2.0 cm long L Ag electrode through a shadow mask at a distance a of 1.0 cm. The structure of the obtained Ag electrodes and the polymer film between these electrodes is electrically isolated from the surrounding polymer film on the substrate by scraping away the polymer with a razor blade to form a rectangular frame. Determine the surface resistance R of the polymer film with an electrometer (Keithley 614) by bringing the Ag electrode into contact with a gold probe.

[0185] The specific resistivity ρ (unit "Ωcm") is calculated using the following formula:

[0186] ρ = R × L × d / a.

[0187] The conductivity σ (unit "S / cm") is calculated using the following formula:

[0188] σ = 1 / ρ

[0189] Determination of particle size (d 50 )

[0190] The particle size is determined as disclosed by H.G. Müller in Colloid Polym. Sci. 267, 1113 - 1116 (1989). The d 50 value of the diameter distribution indicates that 50% of the total weight of all the particles of the conductive polymer in the dispersion can be attributed to those particles having a diameter less than or equal to d 50 value.

[0191] Equivalent series resistance (ESR)

[0192] Determine the equivalent series resistance (in mΩ) at 20 °C at 100 kHz with the aid of an LCR meter (Agilent 4284A). In each capacitor experiment, 2 capacitors have been prepared and the average ESR value has been determined.

[0193] Capacitance (CAP)

[0194] Determine the capacitance at 20 °C at 120 Hz with the aid of an LCR meter (Agilent 4284A). In each capacitor experiment, 2 capacitors have been prepared and the average capacitance value has been determined.

[0195] Surge test

[0196] The capacitors are connected in series to a power supply bank through 100 mOhm resistors and are subjected to a voltage pulse of 18.4 V with a pulse period of 30 s of voltage on (capacitor charging) and 30 s of voltage off (capacitor discharging). The peak current for each charge and discharge is approximately 80 A. One surge cycle consists of a charge and a discharge and has a duration of 60 s. In each capacitor experiment, 2 capacitors have been prepared and the average capacitance value has been determined. Example

[0197] Method step a)

[0198] A porous electrode body for a cylindrical aluminum capacitor having a rated voltage of 16 V (as Figure 2 described) is produced in the following manner.

[0199] The aluminum foil is etched to roughen the surface of the aluminum foil. Then, the aluminum foil is anodized using an aqueous ammonium adipate solution to form a dielectric layer on the surface of the aluminum foil. Thus, an anode foil is produced.

[0200] A second aluminum foil is etched to roughen the surface of the aluminum foil. Thus, a cathode foil is prepared therefrom.

[0201] An anode lead and a cathode lead are respectively connected to the anode and cathode foils. The anode and cathode foils are wound together with two separator papers between the two foils. A tape is placed on the outside of the wound element to prevent the foils from unwinding. Then, the wound element is subjected to another anodization to form a dielectric layer on the cut edge of the anode foil.

[0202] Thus, an anode body including an electrode body having a dielectric layer is prepared.

[0203] Method step b)

[0204] The porous electrode body from method step a) is placed in a chamber of a bath having a liquid composition containing a conductive polymer. The air pressure in the chamber is decreased to 100 hPa. The anode body is immersed in the liquid composition for 300 s. Then, the anode body is extracted from the liquid composition and the chamber is evacuated to atmospheric pressure.

[0205] Method step c)

[0206] The anode body is dried at 120 °C for 30 minutes and then at 150 °C for 30 minutes.

[0207] Method steps b) and c) are carried out one more time. Thus, a capacitor body is obtained.

[0208] Method step d)

[0209] Immerse the capacitor body of method step c) in the impregnation solution for 300 s and then remove it from the impregnation solution.

[0210] Method step e)

[0211] Place the capacitor body of method step d) in a cylindrical aluminum housing and seal it with a rubber seal.

[0212] Method step f)

[0213] Heat the capacitor body of method step e) at 135 °C for 1 hour.

[0214] Preparation Example 1

[0215] Concentrate the poly(3,4-ethylenedioxythiophene) / polystyrenesulfonate aqueous solution (Clevios P VP AI 4083, Heraeus Deutschland) to a solids content of 1.8% and homogenize it 10 times at a pressure of 1500 bar using a high-pressure homogenizer. Adjust the pH of the solution to 6 using ammonia. Thus, a liquid composition containing a conductive polymer is obtained. The conductivity of the liquid composition is determined to be 0.001 S / cm. The d 50 value is 75 nm.

[0216] Preparation Example 2

[0217] Concentrate the poly(3,4-ethylenedioxythiophene) / polystyrenesulfonate aqueous solution (Clevios P VP CH 8000, Heraeus Deutschland) to a solids content of 1.8% and homogenize it 10 times at a pressure of 1500 bar using a high-pressure homogenizer. Mix 99 g of this polymer dispersion and 1 g of dimethyl sulfoxide. Adjust the pH of the solution to 6 using ammonia. Thus, a liquid composition containing a conductive polymer is obtained. The conductivity of the liquid composition is determined to be 0.05 S / cm. The d 50 value is 30 nm.

[0218] Preparation Example 3

[0219] Concentrate the poly(3,4-ethylenedioxythiophene) / polystyrenesulfonate aqueous solution (Clevios PH, Heraeus Deutschland) to a solids content of 1.8% and homogenize it 10 times at a pressure of 1500 bar using a high-pressure homogenizer. Adjust the pH of the solution to 6 using ammonia. Thus, a liquid composition containing a conductive polymer is obtained. The conductivity of the liquid composition is determined to be 0.1 S / cm. The d 50 value is 45 nm.

[0220] Preparation Example 4

[0221] The poly(3,4-ethylenedioxythiophene) / polystyrene sulfonate aqueous solution (Clevios PH 500, Heraeus Deutschland) was concentrated to a solid content of 1.8%, and homogenized 10 times with a high-pressure homogenizer at a pressure of 1500 bar. The pH of the solution was adjusted to 6 using ammonia. Thus, a liquid composition containing a conductive polymer was obtained. The conductivity of the liquid composition was determined to be 0.3 S / cm. The d 50 value was 26 nm.

[0222] Preparation Example 5

[0223] 99.9 g of the liquid composition of Preparation Example 4 and 0.1 g of dimethyl sulfoxide were mixed. Thus, a liquid composition containing a conductive polymer was obtained. The conductivity of the liquid composition was determined to be 3 S / cm.

[0224] Preparation Example 6

[0225] 99.7 g of the liquid composition of Preparation Example 4 and 0.3 g of dimethyl sulfoxide were mixed. Thus, a liquid composition containing a conductive polymer was obtained. The conductivity of the liquid composition was determined to be 9 S / cm.

[0226] Preparation Example 7

[0227] 99.4 g of the liquid composition of Preparation Example 4 and 0.6 g of ethylene glycol were mixed. Thus, a liquid composition containing a conductive polymer was obtained. The conductivity of the liquid composition was determined to be 20 S / cm.

[0228] Preparation Example 8

[0229] 97.5 g of the liquid composition of Preparation Example 4 and 2.5 g of dimethyl sulfoxide were mixed. Thus, a liquid composition containing a conductive polymer was obtained. The conductivity of the liquid composition was determined to be 91 S / cm.

[0230] Preparation Example 9

[0231] 95 g of the liquid composition of Preparation Example 4 and 5 g of ethylene glycol were mixed. Thus, a liquid composition containing a conductive polymer was obtained. The conductivity of the liquid composition was determined to be 306 S / cm.

[0232] Preparation Example 10

[0233] 90 g of the liquid composition of Preparation Example 4 was mixed with 10 g of 1,5-pentanediol. Thus, a liquid composition containing a conductive polymer was obtained. The conductivity of the liquid composition was determined to be 346 S / cm.

[0234] Example 1

[0235] A capacitor was produced in the following manner:

[0236] First, a first anode body according to method step a) was prepared. Then, these anode bodies were treated with the liquid composition containing the conductive polymer of Preparation Example 4 according to method steps b) and c). Method steps b) and c) were carried out one more time. Thus, a capacitor body was obtained.

[0237] Next, the obtained capacitor body was impregnated with ethylene glycol as an impregnating solution according to method step d). The capacitor body was encapsulated according to method step e), and finally heat treatment was carried out according to method step f) to obtain a finished capacitor. The ESR of the capacitor is given in Table 1.

[0238] Example 2

[0239] A capacitor was produced and evaluated in the same manner as in Example 1, however, using diethylene glycol (DEG) as the impregnating solution in method step d). The ESR of the capacitor is given in Table 1.

[0240] Example 3

[0241] A capacitor was produced and evaluated in the same manner as in Example 1, however, using triethylene glycol (TEG) as the impregnating solution in method step d). The ESR of the capacitor is given in Table 1.

[0242] Example 4

[0243] A capacitor was produced and evaluated in the same manner as in Example 1, however, using tetraethylene glycol (TEG) as the impregnating solution in method step d). The ESR of the capacitor is given in Table 1.

[0244] Example 5

[0245] A capacitor was produced and evaluated in the same manner as in Example 1, however, using 1,2-propanediol as the impregnating solution in method step d). The ESR of the capacitor is given in Table 1.

[0246] Example 6

[0247] The capacitor was produced and evaluated in the same manner as in Example 1, however, 1,5-pentanediol was used as the impregnation solution in method step d). The ESR of the capacitor is given in Table 1.

[0248] Comparative Example 1

[0249] The capacitor was produced and evaluated in the same manner as in Example 1, however, dimethyl sulfoxide (DMSO) was used as the impregnation solution in method step d). The ESR of the capacitor is given in Table 1.

[0250] Comparative Example 2

[0251] The capacitor was produced and evaluated in the same manner as in Example 1, however, γ-butyrolactone (GBL) was used as the impregnation solution in method step d). The ESR of the capacitor is given in Table 1.

[0252] Comparative Example 3

[0253] The capacitor was produced and evaluated in the same manner as in Example 1, however, polyethylene glycol 400 (PEG400) was used as the impregnation solution in method step d). The ESR of the capacitor is given in Table 1.

[0254] Table 1

[0255] Impregnation solution ESR [mOhm] Example 1 EG 25 Example 2 DEG 12 Example 3 TEG 13 Example 4 TetraEG 15 Example 5 1,2 - propanediol 18 Example 6 1,5 - pentanediol 17 Comparative Example 1 DMSO 34 Comparative Example 2 GBL 1883 Comparative Example 3 PEG400 31

[0256] Example 7

[0257] The capacitor was produced in the following manner:

[0258] First, a first anode body according to method step a) was prepared. Then, these anode bodies were treated with the liquid composition containing the conductive polymer of Preparation Example 3 according to method steps b) and c). Method steps b) and c) were carried out one more time. Thus, a capacitor body was obtained.

[0259] Next, the obtained capacitor body was impregnated with diethylene glycol as the impregnation solution according to method step d). The capacitor body was encapsulated according to method step e), and finally heat treatment was carried out according to method step f) to obtain the finished capacitor.

[0260] The capacitance of the capacitor was measured before and after a surge test of 1000 surge cycles at 20°C. The relative capacitance after the surge test was calculated according to the following formula:

[0261] (Relative capacitance after the surge test) =

[0262] (Capacitance at 20°C after surge test) / (Capacitance at 20°C before surge test)

[0263] The relative capacitance after the surge test is given in Table 2.

[0264] Example 8

[0265] Capacitors were produced and evaluated in the same manner as in Example 7, however, Preparation Example 4 was used as the conductive polymer. The relative capacitance after the surge test is given in Table 2.

[0266] Example 9

[0267] Capacitors were produced and evaluated in the same manner as in Example 7, however, Preparation Example 5 was used as the conductive polymer. The relative capacitance after the surge test is given in Table 2.

[0268] Example 10

[0269] Capacitors were produced and evaluated in the same manner as in Example 7, however, Preparation Example 6 was used as the conductive polymer. The relative capacitance after the surge test is given in Table 2.

[0270] Example 11

[0271] Capacitors were produced and evaluated in the same manner as in Example 7, however, Preparation Example 7 was used as the conductive polymer. The relative capacitance after the surge test is given in Table 2.

[0272] Example 12

[0273] Capacitors were produced and evaluated in the same manner as in Example 7, however, Preparation Example 8 was used as the conductive polymer. The relative capacitance after the surge test is given in Table 2.

[0274] Comparative Example 4

[0275] Capacitors were produced and evaluated in the same manner as in Example 7, however, Preparation Example 1 was used as the conductive polymer. The relative capacitance after the surge test is given in Table 2.

[0276] Comparative Example 5

[0277] Capacitors were produced and evaluated in the same manner as in Example 7, however, Preparation Example 2 was used as the conductive polymer. The relative capacitance after the surge test is given in Table 2.

[0278] Comparative Example 6

[0279] The capacitor was produced and evaluated in the same manner as in Example 7, however, Preparation Example 9 was used as the conductive polymer. The relative capacitance after the surge test is given in Table 2.

[0280] Comparative Example 7

[0281] The capacitor was produced and evaluated in the same manner as in Example 7, however, Preparation Example 10 was used as the conductive polymer. The relative capacitance after the surge test is given in Table 2.

[0282] Table 2

[0283] Conductivity of the liquid composition [S / cm] Relative capacitance after surge test (1000 cycles) Example 7 0.1 90 Example 8 0.3 100 Example 9 3 96 Example 10 9 94 Example 11 20 87 Example 12 91 84 Comparative Example 4 0.001 59 Comparative Example 5 0.05 64 Comparative Example 6 306 76 Comparative Example 7 346 71

[0284] Example 13

[0285] The capacitor was produced in the following manner:

[0286] First, a first anode body according to method step a) was prepared. Then, these anode bodies were treated with a liquid composition containing the conductive polymer of Preparation Example 4 according to method steps b) and c). Method steps b) and c) were carried out one more time. Thus, a capacitor body was obtained.

[0287] Next, the obtained capacitor body was impregnated with diethylene glycol as the impregnation solution according to method step d). The capacitor body was encapsulated according to method step e), and finally heat treatment was carried out according to method step f) to obtain a finished capacitor.

[0288] The capacitance of the capacitor at 20 °C was measured before and after storing at a storage temperature of 125 °C for 1500 h. The relative capacitance after storing at 125 °C for 1500 h was calculated according to the following formula:

[0289] (Relative capacitance after 1500 h at 125 °C) = (Capacitance at 20 °C after storing at 125 °C for 1500 h) / (Capacitance at 20 °C before storing at 125 °C for 1500 h)

[0290] The relative capacitance (in %) after 1500 h at 125 °C is given in Table 3.

[0291] Example 14

[0292] The capacitor was produced and evaluated in the same manner as in Example 13, however, a mixture of 99 wt% diethylene glycol and 1 wt% tannic acid was used as the impregnation solution. The relative capacitance (in %) after 1500 h at 125 °C is given in Table 3.

[0293] Comparative Example 8

[0294] A capacitor was produced and evaluated in the same manner as in Example 13. However, before method step e), the capacitor body from method step d) was dried at 120 °C for 30 minutes and then at 150 °C for 30 minutes. In addition, method step f) was omitted.

[0295] The relative capacitance (in %) after 1500 h at 125 °C is given in Table 3.

[0296] Table 3

[0297] Relative capacitance after 1500 h at 125°C Example 13 89％ Example 14 93％ Comparative Example 8 76％

[0298] Index of reference numbers

[0299] 1 Porous electrode body

[0300] 2 Electrode material

[0301] 3 Dielectric

[0302] 4 Solid electrolyte

[0303] 5 Pore

[0304] 6 Impregnation solution

[0305] 7 Encapsulation (aluminum housing)

[0306] 8 Capacitor element (porous electrode material coated with dielectric and solid electrolyte and containing an impregnation solvent)

[0307] 9 Rubber seal

[0308] 10 Lead

Claims

1. A method for manufacturing a capacitor, the method comprising the following method steps: a) providing a porous electrode body (1) made of an electrode material (2), wherein a dielectric (3) at least partially covers the surface of the electrode material (2); b) introducing a liquid composition comprising a conductive polymer and a dispersant into at least a part of the porous electrode body (1) provided in method step a), wherein the conductivity of the conductive layer made of the liquid composition is less than 100 S / cm; c) removing at least part of the dispersant from the porous electrode body (1) obtained in method step b) to form a solid electrolyte layer (4) at least partially covering the surface of the dielectric (3); d) filling at least a part of the pores (5) of the porous electrode body (1) obtained in method step c) with an impregnation solution comprising at least one impregnation solvent, wherein the at least one impregnation solvent has a boiling point of at least 150 °C (determined at 1013 hPa); e) encapsulating the porous electrode body (1) obtained in method step d); f) heating the encapsulated electrode body (1) obtained in method step e) at a temperature above 50 °C for more than 10 minutes.

2. The method according to claim 1, wherein the conductive layer made of the liquid composition used in method step b) has a conductivity of not less than 0.1 S / cm.

3. The method according to claim 1 or 2, wherein the conductive polymer in the liquid composition used in method step b) is present in the form of particles, and the diameter d of the particles 50 is in the range of 1 nm to 100 nm.

4. The method according to any one of claims 1 to 3, wherein the conductive polymer in the liquid composition used in method step b) is present in the form of a polythiophene / (poly)anion complex, wherein the polythiophene is poly(3,4-ethylenedioxythiophene) and the polyanion is the anion of polystyrene sulfonic acid.

5. The method according to any one of claims 1 to 4, wherein the liquid composition applied in method step b) contains less than 3% by weight of a high-boiling solvent having a boiling point of at least 150 °C (determined at 1013 hPa).

6. The method according to any one of claims 1 to 5, wherein the at least one impregnation solvent in the impregnation solution applied in method step d) contains at least one hydroxyl group and has a molecular weight in the range of 70 g / mol to 195 g / mol.

7. The method according to any one of claims 1 to 6, wherein the at least one impregnation solvent in the impregnation solution applied in method step d) has a melting point of less than 15 °C.

8. The method according to any one of claims 1 to 7, wherein the impregnation solvent in the impregnation solution applied in method step d) has a boiling point (determined at 1013 hPa) of at least 200 °C and less than 330 °C.

9. The method according to any one of claims 1 to 8, wherein the impregnation solution applied in method step d) has an ionic conductivity of less than 1000 μS / cm.

10. The method according to any one of claims 1 to 9, wherein the at least one impregnation solvent in the impregnation solution applied in method step d) is a polyglycol having 2 to 4 repeating units.

11. The method according to claim 10, wherein the at least one impregnation solvent in the impregnation solution applied in method step d) is selected from the group consisting of diethylene glycol, triethylene glycol, tetraethylene glycol, and mixtures of at least two of them.

12. The method according to any one of claims 1 to 11, wherein the impregnation solution used in method step d) contains a stabilizer.

13. The method according to claim 12, wherein the stabilizer is gallic acid or gallic acid esterified with sugar.

14. Use of a capacitor obtainable by the method according to any one of claims 1 to 13 in an electronic circuit.

15. An electronic circuit, the electronic circuit comprising a capacitor obtainable by the method according to any one of claims 1 to 13.

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