Method for manufacturing a capacitor

Abstract

Method for manufacturing a hybrid polymer aluminium electrolytic capacitor (1) comprising a winding element (2) having a diameter of more than 10 mm and a height of more than 12 mm, comprising the following steps: - Winding an anode foil (3), separators (5), and a cathode foil (4) around an axis to form a winding element (2), - Flooding the winding element (2) with a polymer dispersion, wherein the polymer dispersion contains electrically conductive solid polymer particles or polymer powder and a solvent, - Applying pulses of overpressure lasting from 2 to 20 seconds to the flooded winding element (2).

Description

[0001] The present invention relates to a method for producing a hybrid polymer-aluminum electrolytic capacitor.

[0002] A hybrid polymer-aluminum electrolytic capacitor is an electrolytic capacitor with a liquid electrolyte and a solid electrolyte made of conductive polymer particles. The polymer covers an anode foil, a cathode foil, separators, and tabs that electrically connect the anode foil and the cathode foil. An electrolytic capacitor is a polarized capacitor whose anode is made of aluminum, on which an insulating oxide layer is formed by anodization. The oxide layer acts as the dielectric of the electrolytic capacitor. The non-solid electrolyte or solid polymer covers the surface of the oxide layer and essentially serves as the capacitor's second electrode.

[0003] Hybrid polymer capacitors are described, for example, in US Pat. Nos. 6,307,735 B1 and 7,497,879 B2. Due to the high conductivity of the polymer layer, the equivalent series resistance (ESR) of a hybrid polymer capacitor is low, and its ripple current rate can be high compared to conventional aluminum electrolytic capacitors.

[0004] To date, hybrid polymer capacitors with a diameter of more than 10 mm and a height of more than 12 mm are not available. The main reasons preventing the construction of larger hybrid polymer-aluminum electrolytic capacitors are discussed below.

[0005] Applying the polymer material to a standard winding element design of a conventional aluminum electrolytic capacitor with sizes larger than 10 x 12 mm (diameter x height) results in a reduction in performance in terms of ESR and ripple current capability compared to a parallel connection of several small winding elements with the same total capacitance. If the foils are too large, the current must travel a long distance along the foils, resulting in increased metal resistance. The metal resistance of a conventional winding design is too high to fully utilize the high conductivity of the hybrid polymer electrolyte system. The metal resistance becomes the limiting factor in the ESR.

[0006] Furthermore, prior art methods for impregnating the winding element with a polymer dispersion are described, for example, in US Pat. No. 7,497,879 B2. These methods have a technical limitation regarding the winding height. The polymer dispersion is absorbed into the winding element by the wetting and capillary action of the paper. However, for winding elements with a height of more than 12 mm, it is hardly possible to completely impregnate them using this technology, even if the impregnation process is repeated several times.

[0007] An additional aspect that must be considered when building a highly reliable hybrid polymer-aluminum capacitor is its robustness against charging and discharging.

[0008] Increasing the diameter of a well-known winding element without further design changes makes no sense, since in this case the ESR is higher than that of a parallel connection of two small capacitors with the small total capacitance.

[0009] Increasing the height of a conventional winding element without further process modifications also makes no sense due to the technical limitations of the prior art polymer impregnation process discussed above. During polymer impregnation, the liquid must reach, cover, and penetrate every part of the winding element. This is hardly possible and definitely inefficient for winding heights exceeding 12 mm when applying the standard process described in US Pat. No. 7,497,879 B2. The polymer dispersion used in hybrid polymer capacitors is very viscous. Impregnation of windings longer than 12 mm is not possible with conventional immersion treatment due to the high viscosity of the polymer dispersion. In this case, the homogeneity of the polymer dispersion within the winding is insufficient, and the central part of the separation even remains dry.The result would be an improper electrical connection between the cathode foil and the anode foil.

[0010] The polymer is mostly bonded to the oxide of the anode foil and the thin oxide of the cathode foil. During the capacitor's voltage change, the polymer potential is mostly close to the cathode foil potential because the cathode oxide is very thin. On the other hand, in hybrid polymer capacitors currently on the market, only a few polymer regions are in contact with the anode foil. In this region, only the potential of the anode foil dominates. Therefore, compensation currents are generated. If the voltage change is too rapid, the resulting compensation current can destroy the polymer and cause short circuits.

[0011] Further information on the state of the art can be found in DE 42 13 651 A1, DE 11 2004 000 061 T5, US 3 681 666 A or DE 100 03 261 A1.

[0012] In addition, reference is made in particular to JP 2001 - 155 966 ​​A, which describes the state of the art regarding impregnation processes for polymer dispersions for solid electrolytic capacitors.

[0013] The object of the present invention is to overcome the problems of the prior art that prevent the construction of a hybrid polymer-aluminum electrolytic capacitor with larger dimensions. This problem is solved by the present claim 1 and the further independent claims.

[0014] It is another object of the present invention to provide an improved capacitor.

[0015] It is another object of the present invention to provide a method that enables the construction of such a capacitor.

[0016] According to a first aspect not according to the invention, a hybrid polymer-aluminum electrolytic capacitor is described which has a winding element which has a diameter of more than 10 mm and a height of more than 12 mm.

[0017] As discussed above, a hybrid polymer-aluminum electrolytic capacitor is an electrolytic capacitor with a liquid electrolyte and a solid electrolyte made of conductive polymer particles. The polymer covers an anode foil, a cathode foil, separators, and tabs that electrically connect the anode foil and the cathode foil. The anode foil, the cathode foil, and the separator are wound to form the winding element.

[0018] Therefore, the winding element may comprise an anode foil and a cathode foil wound around an axis with separators arranged between the anode foil and the cathode foil, wherein the anode foil, the cathode foil, and the separators are covered with a conductive polymer, and wherein the capacitor comprises a liquid electrolyte.

[0019] The anode foil may comprise an aluminum foil with an oxide layer disposed on the surface of the aluminum foil. The oxide layer may be formed by oxidation after roughening the surface of the aluminum foil. The oxide layer may act as a dielectric coating film. Furthermore, the cathode foil may also be an aluminum foil having an oxide layer on its surface. The oxide layer on the cathode foil may also be formed by oxidation after roughening the surface. The cathode foil may have a smaller thickness than the anode foil. The oxide layer on the cathode foil may be thinner than the oxide layer on the anode foil.

[0020] Each of the separators can be paper. The separators are impregnated with the polymer. The separator can also be impregnated with a liquid electrolyte. In particular, the winding element can have two separators, each impregnated with the polymer.

[0021] The winding element can have a cylindrical shape. The height of the winding element corresponds to the height of the cylindrical shape. The height can sometimes also be referred to as the length of the winding element. The diameter of the winding element can correspond to the diameter of the cylindrical shape.

[0022] A winding element with a diameter of more than 10 mm and a height of more than 12 mm offers the advantages of low ESR and high ripple current capability. As described later, the inventors have found a way to enable the construction of a large-sized hybrid polymer-aluminum electrolytic capacitor.

[0023] The anode foil, the cathode foil, and the separators can be covered with a conductive polymer. In addition, tabs that electrically connect the anode foil to the cathode foil can also be covered with the conductive polymer. The conductive polymer cover can be formed by impregnating the winding element with a polymer dispersion. The polymer dispersion can comprise a solvent and either conductive polymer particles or a conductive polymer powder. In addition to the polymer, the hybrid polymer-aluminum electrolytic capacitor comprises a liquid electrolyte.

[0024] The capacitor can be an axial capacitor. Hybrid polymer-aluminum electrolytic capacitors, which are axial capacitors, have several advantages. For example, a multi-tab connection is possible for an axial capacitor. In particular, a multi-tab connection for an axial capacitor is possible over a very wide range of diameters. A multi-tab connection means that at least two tabs are connected to the anode foil, allowing a potential to be applied to the anode foil at two points, and at least two tabs are connected to the cathode foil, allowing a potential to be applied to the cathode foil at two points. The use of a multi-tab connection allows the length the current must travel along the foil to be reduced compared to a single-tab connection, where the potential is applied to the foils at only one point.This allows the resistance of the anode foil and the resistance of the cathode foil to be reduced.

[0025] In addition, an axial capacitor provides a symmetrical structure.

[0026] The anode foil and the cathode foil can be arranged and dimensioned such that, in the winding element, every part of the anode foil is covered by the cathode foil. Accordingly, the winding element can have no polymer region that borders only the anode foil and not the cathode foil. The winding element can be free of polymer regions in which the potential of the polymer region is dominated by the potential of an anode foil. Accordingly, the occurrence of compensation currents can be prevented. The capacitor can be wound in such a way that the polymer regions all border the cathode foil, so that the cathode foil always dominates the potential of the polymer. Accordingly, all polymer regions have the same potential, i.e., the potential of the cathode foil. Therefore, no compensation current can occur in the polymer regions.Preventing such compensation currents can help increase the reliability and service life of the capacitor. Compensating currents can destroy the polymer and cause short circuits. Therefore, this problem can be avoided by preventing compensation currents.

[0027] The cathode foil may comprise an aluminum foil covered with an oxide layer, the oxide layer on the cathode foil having a uniform thickness. By avoiding asymmetry in the thickness of the oxide layer on the cathode foil, compensation currents can be avoided even during charging and discharging of the capacitor. The thickness of the oxide layer can be considered uniform if the minimum thickness of the oxide layer is no thinner than 10 nm.

[0028] The winding element can be arranged within a can with a can base. The can can comprise a conductive material. The cathode foil can have a greater extension in the axial direction toward the can base than the anode foil, with the cathode foil being in electrical contact with the can base.

[0029] This design is also called an extended cathode foil. The extended cathode foil is particularly advantageous for a hybrid polymer-aluminum electrolytic capacitor. In an electrolytic capacitor that does not have a solid polymer, an extended cathode foil leads to problems due to oxidation that occurs on the extended cathode foil over the lifetime of the capacitor. However, in the hybrid polymer capacitor, the cathode foil is covered with a polymer that can prevent oxidation. Therefore, no performance degradation is produced if the oxidation of the extended cathode foil is prevented.

[0030] The can bottom may have a structure that mechanically impedes movement of the winding element relative to the can bottom. The structure may, for example, have ribs. The structure and the extending cathode foil may be arranged and shaped such that the foil and the structure fuse together, thereby preventing relative movement of the cathode foil relative to the can bottom.

[0031] The cathode foil can also be welded to the bottom of the can.

[0032] The can may include a corrugation that secures the winding element. The corrugation may be an inwardly projecting portion of the can.

[0033] The can may have a cover. The anode foil may have a greater extension in the axial direction toward the lid than the cathode foil, with the anode foil being electrically connected to the cover. The cover may also have a structure similar to the structure discussed above with respect to the can bottom. The anode foil and the structure on the cover may be arranged and adapted to interlock. Relative movement of the anode foil and the can may be prevented by the interlocking of the anode foil and the cover. The structure of the cover may, for example, have ribs. The anode foil may be welded to the cover.

[0034] The capacitor may have at least two tabs that are electrically connected to the anode foil and at least two tabs that are electrically connected to the cathode foil. This design is also known as a multi-tab connection. A multi-tab connection is particularly simple for axial capacitors. A multi-tab connection can provide the advantage of reduced resistance because a potential can be applied to each foil at multiple points. This can reduce the metallic resistance of the foil.

[0035] The winding element may have a diameter of less than 22 mm. Preferably, the winding element has a diameter in the range of 12 mm to 17 mm. The winding element may have a height of less than 40 mm. Preferably, the winding element has a height in the range of 15 mm to 30 mm.

[0036] The ratio of the height of the winding element to the diameter can be greater than 2. This ratio leads to particularly preferred electrical properties of the winding element.

[0037] Furthermore, a hybrid polymer-aluminum electrolytic capacitor is described, which has a first winding element and a second winding element. The first winding element has an anode, separators, and a cathode foil wound around an axis and covered by a conductive polymer. In addition to the conductive polymer, the first winding element has a liquid electrolyte. The first winding element has a height of more than 12 mm. The second winding element has an anode foil, separators, and a cathode foil wound around an axis and covered by a conductive polymer. In addition to the conductive polymer, the second winding element has a liquid electrolyte. The second winding element has a height of more than 12 mm. The winding elements are arranged in a common can.Each winding element has a tab connected to its anode foil and a tab connected to its cathode foil. The tabs connected to the anode foils are connected to each other, and the tabs connected to the cathode foils are connected to each other, so that the winding elements are electrically connected in parallel. The capacitor may further comprise more than two winding elements, each winding element being designed in the same manner as the first and second winding elements and all of the winding elements being arranged in the common can. Each of the first winding element and the second winding element may be a radial winding element. Alternatively, each of the first winding element and the second winding element may be an axial winding element.

[0038] The capacitor may have more than two winding elements arranged in the common can and connected in parallel to each other.

[0039] The winding elements are manufactured using the impregnation process described below, which enables homogeneous impregnation, even for winding elements with a height greater than 12 mm.

[0040] The present invention relates to a method for producing the capacitor according to the first aspect. The method comprises the steps according to claim 1, in particular the following steps: - Winding an anode foil, separators, and a cathode foil around an axis to form a winding element, - flooding the winding element with a polymer dispersion, wherein the polymer dispersion contains electrically conductive solid polymer particles or polymer powder and a solvent, - Applying pulses of overpressure to the flooded winding element.

[0041] By using pulses of overpressure, the polymer dispersion can be distributed homogeneously throughout the entire winding element. This process makes it possible to impregnate internal parts of the winding element that could previously not be reached by impregnation.

[0042] During a pulse of overpressure, an overpressure in the range of 2 to 150 bar can be applied, followed by the application of either atmospheric pressure or a pressure of less than 1 bar. The pulses are preferably applied multiple times.

[0043] Additionally, the method may include the step of placing the winding element in a can containing a liquid electrolyte.

[0044] In another aspect, the present invention relates to an alternative method for manufacturing the capacitor. The method comprises the following steps: - Winding an anode foil, separators, and a cathode foil around an axis to form a winding element, - Arranging the winding element in a tube, - Forcing a polymer dispersion to flow through the tube and thereby through the winding element, wherein the polymer dispersion contains electrically conductive solid polymer particles or polymer powder and a solvent.

[0045] An overpressure of at least 1.5 bar can be applied when the polymer dispersion flows through the winding element. The flow-through process also ensures that the large-sized winding element is homogeneously impregnated. Applying the overpressure further improves the flow-through process.

[0046] Additionally, the method may include the step of placing the winding element in a can containing a liquid electrolyte.

[0047] The present invention will be described in detail below. Fig. 1 shows a first embodiment of a winding element. Fig. Figure 2 shows different types of capacitors in a perspective view. Fig. 3 shows a capacitor having three winding elements. Fig. Figure 4 shows an X-ray image of a conventional polymer electrolytic capacitor. Fig. Figure 5 shows a schematic cross-sectional view of a hybrid aluminum polymer electrolytic capacitor without lead tabs. Fig. Figure 6 shows an example of a polymer dispersion applied to a winding element using a conventional impregnation process. Fig. Figure 7 shows a detailed photograph of a winding element impregnated with the new process. The Fig. Figures 8 to 12 show different types of capacitor elements.

[0048] The Fig. 1 shows a first embodiment of a winding element 2 of a hybrid polymer-aluminum electrolytic capacitor 1. The winding element 2 has a diameter of more than 10 mm and a height of more than 12 mm.

[0049] The winding element 2 comprises an anode foil 3, a cathode foil 4, and a separator 5, which are wound around a common axis. The separator 5 is arranged between the anode foil 3 and the cathode foil 4. The winding element 2 further comprises a further separator, which is also arranged between the anode foil 3 and the cathode foil 4 and which Fig. 1 is not shown to simplify the figure. Specifically, the anode foil 3, the separator 5, the cathode foil 4, and the other separator are stacked in this order and then wound around the axle.

[0050] The winding element 2 was impregnated with a polymer 6. The impregnation is Fig. 1 by showing an enlarged view of the polymer 6 covering the anode foil 3, the cathode foil 4, and the separator 5. The polymer 6 covering the anode foil 3, the cathode foil 4, and the separators 5 is conductive. In addition to the polymer, the capacitor 1 also includes a liquid electrolyte.

[0051] The anode foil 3 comprises an aluminum foil. The surface of the aluminum foil was roughened by an etching process, and then a dielectric oxide film was formed on the surface by an oxidation treatment. Therefore, the anode foil 3 comprises an aluminum foil with an oxide layer on its surface. The cathode foil 4 also comprises an aluminum foil on which the surface of the aluminum foil was roughened by an etching process, and then a dielectric oxide film was formed on the surface by an oxidation treatment. Therefore, the cathode foil 4 also comprises an aluminum foil with an oxide layer on its surface.

[0052] The anode foil 3 and the cathode foil 4 are dimensioned such that, when wound, they result in a winding element 2 with a diameter of more than 10 mm and a height of more than 12 mm. Therefore, the foils 3 and 4 are larger and wider than the foils conventionally used for hybrid polymer-aluminum electrolytic capacitors.

[0053] Each of the separators 5 is a paper impregnated with the polymer 6.

[0054] The common axis around which the winding element 2 is wound defines an axial direction.

[0055] The winding element 2 further comprises tabs 7, 8, which serve to electrically contact the winding element 2. The winding element 2 has two tabs 7, both of which are connected to the anode foil 3. The tabs 7 connected to the anode foil 3 extend in the positive axial direction. Furthermore, the winding element 2 has two tabs 8, which are connected to the cathode foil 4. The tabs 8 connected to the cathode foil 4 extend in the negative axial direction, i.e., in the opposite direction to the tabs 7 connected to the anode foil 3.

[0056] Capacitors 1 with tabs 7 connected to the anode foil 3 and tabs 8 connected to the cathode foil 4 extending in opposite directions are also known as axial capacitors. In contrast, in a radial capacitor, a tab connected to the anode foil and a tab connected to the cathode foil both extend in the same axial direction, i.e., both extend in the positive axial direction or both extend in the negative axial direction.

[0057] The use of multiple tabs 7, 8 to connect each of the anode foils 3 and the cathode foil 4 allows the use of long and wide foils 3, 4. The use of multiple tabs 7, 8 reduces the metal resistance of the winding element 2 because a current can be fed into the winding element 2 at multiple points, thereby reducing the distance the current must travel in the winding element 2. The use of multiple tabs 7, 8 is not known from hybrid polymer-aluminum electrolytic capacitors.

[0058] Fig. Figure 2 shows different types of capacitors in a perspective view. In particular, Fig. 2 two axial capacitors 9, each of which has two tabs 7 extending in the positive axial direction and two tabs 8 extending in the negative axial direction. The tabs 7 extending in the positive axial direction are connected to the anode foil 3, and the tabs 8 extending in the negative axial direction are connected to the cathode foil 4. For the axial capacitor shown on the left, the two tabs 8 are not visible due to the perspective.

[0059] The winding element of the axial capacitor 9 is wound around an axis. Each of the two tabs 7 connected to the anode foil 3 is arranged at a radial distance from this axis. In a plane perpendicular to the axis, the two tabs 7 are arranged point-symmetrically with respect to the axis. Each of the two tabs 8 connected to the cathode foil 4 is arranged at a radial distance from the axis. In a plane perpendicular to the axis, the two tabs 8 are arranged point-symmetrically with respect to the axis. The axial capacitors 9 with two tabs 7, 8 connected to each of the anode foil 3 and the cathode foil 4 have a low ESR and thus an increased ripple current capacity.

[0060] It can be seen that building a capacitor with two tabs connected to each of the anode foil and the cathode foil is possible for an axial capacitor 9. Fig. 2 further shows two snap-in capacitors 10. A minimum diameter of 22 mm is required to enable the construction of a snap-in capacitor 10 with two tabs connected to each of the anode foil 3 and the cathode foil 4. Fig. 2 further shows a radial capacitor 11. It is not possible to build a radial capacitor 11 with two tabs, each connected to the anode foil 3 and the cathode foil 4.

[0061] The Fig. The capacitor 1 shown in Figure 1 is arranged inside a box which is Fig. 1 is not shown. The can comprises a tubular can body, a can bottom, and a cover. The can bottom and the cover are disc-shaped. In the axial direction, the tubular can body is arranged between the can bottom and the cover.

[0062] The cathode foil 4 has a greater extension in the axial direction towards the can bottom than the anode foil 3. The separators 5 have a smaller extension in the axial direction towards the can bottom than the cathode foil 4. The anode foil 3 has a smaller extension in the axial direction towards the can bottom than the cathode foil 4 and the separators 5.

[0063] The extending cathode foil 4 touches the can bottom. Therefore, a current can flow through a short circuit via the conductive housing bottom to the cathode foil 4. The Fig. The extending cathode foil 4 shown in Figure 1 results in a reduced ESR.

[0064] This idea is familiar from electrolytic capacitors, where the winding element is mechanically pressed against the can bottom so that an extended cathode foil touches the can bottom. This approach works with low reliability and only for a limited time. During operation, an oxide layer forms between the cathode foil and the can bottom, reducing and eventually breaking the electrical connection.

[0065] However, in the hybrid polymer-aluminum electrolytic capacitor 1, the cathode foil 4 is covered with a polymer. The polymer coating prevents oxidation of the cathode foil 4. Therefore, no oxide layer can grow. In addition, the polymer is also conductive, so that a current can flow from the can bottom via the polymer to the cathode foil 4. Accordingly, no connection between two metals is required. Therefore, the Fig. 1 results in better thermal connection and reduced ESR.

[0066] For long-term stability of the electrical connection to the can, mechanical movement of the winding element 2 relative to the can should be prevented. Therefore, the cathode foil 4 can be attached to the can base, e.g., by welding. Welding has the advantage of low contact resistance but has the disadvantage of an additional process step and therefore additional costs.

[0067] Alternatively or additionally, the can bottom may further include a structure, e.g., ribs. The structure may further help prevent mechanical movement. The structure may be designed to fix the extending cathode foil 4 in place. For example, the cathode foil 4 may be clamped between two adjacent ribs. The cathode foil 4 and the structure on the can bottom may be designed to interlock, thereby providing mechanical stability.

[0068] In addition, the can may have a corrugation, which also mechanically secures the winding element 2. The corrugation may be an inwardly protruding part of the can. The corrugation holds the winding element 2 securely to the can base. Therefore, the current path from the can base to the cathode foil 4 remains stable via the polymer or via a metal connection.

[0069] Additionally or alternatively, the anode foil 3 can extend in the opposite direction. Accordingly, the extended anode foil 3 can contact the cover of the can. The extended anode foil 3 can be welded to the cover. This solution provides a low equivalent ESR, as is the case with a high number of tabs on the anode side.

[0070] Fig. 3 shows another embodiment of a capacitor 1 having three winding elements 2, each winding element 2 having a height of more than 12 mm. Each winding element is connected by two tabs 7, 8, one tab 7 being connected to the anode foil 3 and one tab 8 being connected to the cathode foil 4. All tabs 7 connected to the anode foils 3 are connected to one another. Furthermore, all tabs 8 connected to the cathode foils 4 are also connected to one another. Therefore, the winding elements 2 are electrically connected in parallel. The winding elements 2 are arranged in a common can 12. All tabs 7, 8 are pulled out on the same side. Therefore, each winding element 2 is connected as a radial winding element. All tabs 7 connected to the anode foils 3 are connected to one another. Furthermore, all tabs 8 connected to the cathode foils 4 are also connected to one another.

[0071] In an alternative design, the winding elements 2 may be formed as axial winding elements, wherein the tabs 7 connected to the anode foil are pulled out at one end of the winding elements 2 and the tabs 8 connected to the cathode foil are pulled out at the opposite end of the winding element 2.

[0072] Fig. Figure 4 is an X-ray image of a conventional polymer electrolytic capacitor. Figure 4 explains a failure mechanism that has been identified.

[0073] The polymer is mostly connected to the oxide of the anode foil 3 and the oxide of the cathode foil 4. During a voltage change of the capacitor, the polymer potential is mainly close to the potential of the cathode foil because the oxide on the cathode foil 4 is very thin.

[0074] However, the capacitor also has polymer regions that are only in contact with the anode foil 3. These regions are indicated by two thick arrows A in Fig. 4. In this area, only the potential of the anode foil 3 dominates. Therefore, compensation currents are generated when the capacitor is charged or discharged. Furthermore, if the voltage charge is too fast, the resulting compensation current can destroy the polymer and cause short circuits. As will now be explained, the anode foil 3 and the cathode foil 4 are dimensioned and wound in such a way that compensation currents can be avoided.

[0075] Fig. Figure 5 shows a schematic cross-sectional view of the hybrid polymer-aluminum electrolytic capacitor 1. The capacitor 1 comprises the anode foil 3, the cathode foil 4, a first separator 5, and a second separator 5. Furthermore, the capacitor 1 comprises a liquid electrolyte 13 that fills the gaps between the anode foil 3, the cathode foil 4, and the separators 5.

[0076] The anode foil 3 is shorter than the cathode foil 4. Therefore, the winding element 2 does not have the anode foil 3 at the beginning and end of its winding. In every part of the winding element 2, the cathode foil 4 is always parallel to the anode foil 3. The winding element 2 has no region in which the anode foil 3 is free of the cathode foil 4. The winding element 2 has no polymer region that is in contact with the anode foil 3 and not in contact with the cathode foil 4. The anode foil 3 and the cathode foil 4 are arranged and dimensioned such that in the winding element 2, every part of the anode foil 3 is covered by the cathode foil 4.

[0077] Therefore, it can be ensured that the capacitor 1 does not have a polymer region in which the potential applied to the anode foil 3 can dominate the potential in an adjacent polymer region. Accordingly, no compensation current can be generated. The arrangement of the cathode foil 4 ensures that the polymer and the electrolyte 13 have more or less the same electrical potential. The Fig. The error mechanism discussed in section 4 can be avoided.

[0078] In addition, an inhomogeneous thickness of the oxide layer on the cathode foil 4 can also lead to compensation currents during charging and discharging of the capacitor 1. To avoid the generation of the compensation current, the oxide layer on the cathode foil 4 has a homogeneous thickness. Therefore, the thickness of the oxide layer is considered homogeneous if its minimum thickness is not thinner than 95% of its maximum thickness.

[0079] The homogeneous oxide thickness on the cathode foil 4 further increases robustness against transient electrical loads. This can be achieved by using cathode foils 4 formed up to a voltage level of, for example, 3 V or more, instead of applying unformed foils with a lower and naturally varying oxide thickness.

[0080] The following describes the process for impregnating the winding element 2 with a polymer dispersion. The winding element 2 is wound prior to the step of impregnating the winding element 2.

[0081] The polymer dispersion comprises electrically conductive solid polymer particles or a polymer powder. The polymer dispersion also contains a solvent, e.g., water. Prior art discloses methods for impregnating a winding element 2 with a polymer dispersion, wherein the polymer dispersion is applied under vacuum conditions. As already discussed, this method has technical limitations regarding the height of the winding element 2. Fig. Figure 6 shows an example of a polymer dispersion applied to a winding element 2 with a height of more than 10 mm using a conventional impregnation process. Fig. Figure 6 clearly shows that the polymer solution only penetrates the upper and lower parts of the separator, the anode foil, and the cathode foil. The middle part of the separator is completely free of polymer, as the polymer particles could not penetrate using a strong vacuum.

[0082] In contrast, according to the present invention, the winding element 2 can be impregnated with a polymer dispersion using pressure pulses of overpressure. The winding element 2 is arranged in a tightly sealed pressure vessel. The vessel is flooded with a polymer dispersion through a connecting piece. Overpressure air is applied to the vessel through the connecting piece. The overpressure air can have a pressure of more than 1.013 bar (1 atm). The overpressure can range from 2 to 150 bar. The overpressure is released after a few seconds, according to the invention after a period in the range of 2 seconds to 20 seconds. The pressure in the vessel then drops to a lower pressure. The lower pressure can be either atmospheric pressure or a pressure below 1 bar. The cycle of applying overpressure followed by applying a lower pressure is considered a pressure pulse. The cycle is repeated several times.By applying pressure pulses to the winding element and the polymer dispersion, the polymer dispersion is distributed in a homogenized manner in the anode foil 3, the separator 5, and the cathode foil 4.

[0083] The Fig. Figure 7 shows a detailed photograph of an anode foil 3, a separator 5, and a cathode foil 4, which were impregnated using pressure pulses. The polymer particles have reached the core of the separator 5. The penetration of the polymer particles into the winding element 2 and the homogeneity of the polymer distribution are excellent.

[0084] In an alternative process, the winding elements 2 are arranged in a tube, and the tube is filled with the polymer dispersion flowing through the tube and thus through the winding elements 2. Furthermore, an overpressure of more than 1.5 bar can be applied to the polymer dispersion. This process also results in a homogeneous coverage of the anode foil 3, the separator 5, the cathode foil 4, and the tabs 7, 8 with the polymer. In particular, the polymer dispersion enters the bottom or top of the winding element 2 and flows through the winding element 2 in the axial direction. The process can be designed so that the polymer dispersion circulates and therefore flows through the winding element 2 several times, each time further improving the impregnation of the winding element 2.

[0085] The methods for impregnating the winding element 2 described above enable homogeneous impregnation of winding elements 2 with a diameter of more than 10 mm and a height of more than 12 mm.

[0086] The hybrid polymer-aluminum electrolytic capacitor described above has the following advantages. Even with diameters larger than 10 mm, it provides a low ESR and therefore a high ripple current capability. Since the capacitor has a height of more than 12 mm, it has a low ESR. Furthermore, the diameter of more than 10 mm and the height of more than 12 mm result in a high capacitance. The low ESR and the large dimensions further result in a high ripple current capability. Even with high-voltage ripple loads, high quality can be ensured. Therefore, a customer can use a smaller number of large capacitors instead of a larger number of small ones. The service life of the hybrid polymer-aluminum electrolytic capacitor is long due to its large dimensions.The capacitor has a large reservoir of liquid electrolyte, which therefore escapes more slowly by diffusion through the rubber and can materials.

[0087] The Fig. Figures 8 to 12 show different designs of the capacitor having a winding element with a diameter of more than 10 mm and a length of more than 12 mm. Each of the Fig. The capacitors shown in Figures 8 to 12 are hybrid polymer-aluminum electrolytic capacitors. Fig. Figure 8 shows an axial capacitor. It is designed for soldering or welding leads. Fig. Figure 9 shows a soldering star capacitor. A soldering star capacitor provides the advantage of low inductance. Fig. 10 shows a flat horizontal solder star capacitor. Fig. Figure 11 shows a surface mount capacitor. Fig. 12 shows a press-fit version of either the Fig. 9 or the capacitor shown in Fig.10 shown capacitor. Reference symbol 1 capacitor 2 winding element 3 anode foil 4 Cathode foil 5 Separator 6 Polymer 7 tab 8 tab 9 Axial capacitor 10 Snap-in capacitor 11 Radial capacitor 12 cans 13 liquid electrolyte

Claims

[1] A method for producing a hybrid polymer-aluminum electrolytic capacitor (1) having a winding element (2) having a diameter of more than 10 mm and a height of more than 12 mm, comprising the following steps: - Winding an anode foil (3), separators (5), and a cathode foil (4) around an axis to form a winding element (2), - flooding the winding element (2) with a polymer dispersion, wherein the polymer dispersion contains electrically conductive solid polymer particles or polymer powder and a solvent, - Applying pulses of overpressure with a duration of 2 to 20 seconds to the flooded winding element (2). [2] A method according to the preceding claim, wherein during a pulse of overpressure an overpressure in the range of 2 to 150 bar is applied, followed by either an atmospheric pressure or a pressure below 1 bar. [3] A method for producing a hybrid polymer-aluminum electrolytic capacitor (1) having a winding element (2) having a diameter of more than 10 mm and a height of more than 12 mm, comprising the following steps: - Winding an anode foil (3), separators (5), and a cathode foil (4) around an axis to form a winding element (2), - arranging the winding element (2) in a tube, - forcing a polymer dispersion to flow through the tube and thereby through the winding element (2), wherein the polymer dispersion contains electrically conductive solid polymer particles or polymer powder and a solvent. [4] Method according to the preceding claim, wherein an overpressure of at least 1.5 bar is applied when the polymer dispersion flows through the winding element (2). [5] Method according to one of the preceding claims, wherein the winding element (2) comprises an anode foil (3) and a cathode foil (4) wound around an axis, with separators (5) arranged between the anode foil (3) and the cathode foil (4), wherein the anode foil (3), the cathode foil (4), and the separators (5) are covered with a conductive polymer (6), and wherein the capacitor (1) has a liquid electrolyte (13). [6] Method according to one of the preceding claims, wherein the capacitor (1) is an axial capacitor. [7] Method according to one of the preceding claims, wherein the anode foil (3) and the cathode foil (4) are arranged and dimensioned such that in the winding element (2) each part of the anode foil (3) is covered by the cathode foil (4). [8] Method according to one of the preceding claims, wherein the cathode foil (4) comprises an aluminum foil covered with an oxide layer, the oxide layer having a homogeneous thickness on the cathode foil (4). [9] Method according to one of the preceding claims, wherein the winding element (2) is arranged within a can (12) having a can bottom, wherein the cathode foil (4) has a greater extent in the axial direction, towards the can bottom, than the anode foil (3) and wherein the cathode foil (4) is electrically contacted with the can bottom. [10] Method according to the preceding claim, wherein the can bottom has a structure which mechanically hinders movement of the winding element (2) relative to the can bottom. [11] Method according to one of claims 9 or 10, wherein the cathode foil (4) is welded to the can bottom. [12] Method according to one of claims 9 to 11, wherein the can (12) has a corrugation fixing the winding element (2). [13] Method according to one of claims 9 to 12, wherein the can (12) has a cover, wherein the anode foil (3) has a greater extent in the axial direction, towards the cover, than the cathode foil (4) and wherein the anode foil (3) is electrically contacted with the cover. [14] Method according to the preceding claim, wherein the anode foil (3) is welded to the cover. [15] Method according to one of the preceding claims, wherein the capacitor (1) has at least two tabs (7) electrically contacted with the anode foil (3) and at least two tabs (8) electrically contacted with the cathode foil (4). [16] Method according to one of the preceding claims, wherein the winding element (2) has a diameter of less than 22 mm. [17] Method according to one of the preceding claims, wherein the ratio of the height of the winding element (2) to the diameter of the winding element (2) is greater than 2. [18] Method for producing a capacitor (1) comprising the following steps: - Winding an anode foil (3), separators (5), and a cathode foil (4) around an axis to form a winding element (2), - flooding the winding element (2) with a polymer dispersion, wherein the polymer dispersion contains electrically conductive solid polymer particles or polymer powder and a solvent, - applying pulses of overpressure with a duration of 2 to 20 seconds to the flooded winding element (2), wherein the capacitor is a hybrid polymer-aluminum electrolytic capacitor (1), comprising a first winding element (2) comprising an anode foil (3), separators (5), and a cathode foil (4) wound around an axis and covered by a conductive polymer (6), wherein the first winding element (2) comprises a liquid electrolyte (13), and a second winding element (2) comprising an anode foil (3), separators (5), and a cathode foil (4) wound around an axis and covered by a conductive polymer (6), wherein the second winding element (2) comprises a liquid electrolyte (13), wherein the first winding element (2) and the second winding element (2) have a height of more than 12 mm, wherein the winding elements (2) are arranged in a common box (12), wherein each winding element (2) has a tab connected to the respective anode foil (3) and a tab connected to the respective cathode foil (4), and wherein the tabs (7) connected to the anode foils (3) are connected to one another and the tabs (8) connected to the cathode foils (4) are connected to one another, so that the winding elements (2) are electrically connected in parallel to one another. [19] A method according to the preceding claim, wherein during a pulse of overpressure an overpressure in the range of 2 to 150 bar is applied, followed by either an atmospheric pressure or a pressure below 1 bar. [20] Method according to claim 18 or 19, wherein each of the first winding element (2) and the second winding element (2) is a radial winding element, or wherein each of the first winding element (2) and the second winding element (2) is an axial winding element.

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