Metallized substrate electrode and electrolytic capacitor using same

Abstract

An electrode for an electrolytic capacitor, preferably a wound electrolytic capacitor, is provided, the electrode comprising a carrier substrate and a first metallization on a first side of the carrier substrate.

Description

FIELD OF THEINVENTION

[0001] The present specification relates to an electrode and an electrolytic capacitor having the electrode.

[0002] Electrolytic capacitors, particularly wound electrolytic capacitors, are of great importance in a variety of technologies for short-term storage of electrical energy or other applications.

[0003] There is a continuing demand for improved volumetric efficiency in electrolytic capacitors, which means that the capacitors become smaller while maintaining the same capacitance, i.e., the capacitors maintain their size but achieve increased capacitance.

[0004] However, in the case of conventional wound electrolytic capacitors with etched aluminum cathodes and anodes and separators between the cathode and anode, possible improvements are hindered by physical constraints related to both the manufacturing process and the functional requirements of wound electrolytic capacitors.

[0005] US Pat. No. 7,990,681 and US Patent Application Publication No. 2004 / 0100756 describe electrolytic capacitors in which the thickness of the cathode is in the range of 15-60 μm, or even up to 80 μm.

[0006] The problem to be solved by the present invention is to improve the capacitors known from the prior art and to disclose a cathode suitable for the improved capacitors.

[0007] The above object can be achieved at least in part by an electrode according to claim 1 or a capacitor comprising such an electrode.

[0008] In a first aspect, an electrode for an electrolytic capacitor, preferably a wound electrolytic capacitor, is described. The electrode comprises a carrier substrate and a first metallization on a first side of the carrier substrate. It is particularly preferred that the first metallization is formed on the first side of the carrier substrate. It is therefore also particularly preferred that the first metallization is attached to or glued to the first side of the carrier substrate.

[0009] The electrode structure according to the first aspect is preferably applied to a cathode suitable for a wound electrolytic capacitor. The electrode is most preferably a cathode. This means that the principles described below relate specifically to the cathode. However, the principles described herein may be equally applicable to the anode of a wound electrolytic capacitor.

[0010] The electrodes may be in the form of a foil. In particular, the electrodes may be electrode foils. As a result, it is preferred that the metallized carrier substrate is also in the form of a foil. The carrier substrate may be a carrier substrate foil.

[0011] The above electrodes allow for the production of more volumetrically efficient electrolytic capacitors, especially when the electrode is a cathode.

[0012] The teachings of the present invention are preferably applicable to cathodes, since the inventors have found that a thin metal coating in the range of 0.01 to 1 μm thickness may be sufficient to replace the function of a conventional cathode, whereas in the case of a conventional anode, a thicker metal coating would be more advantageous to allow for the formation of deep etching structures or oxide layers.

[0013] The inventors have found that conventional electrodes, particularly conventional cathodes made of aluminum for wound electrolytic capacitors, require a relatively thick, unetched core to provide sufficient stability and tensile strength to be handled in state-of-the-art roll-to-roll processes. Otherwise, electrodes constructed accordingly may tear or crack. Thus, conventional cathodes made of etched aluminum are almost impossible to make thinner than 15 μm in order to be handled in state-of-the-art roll-to-roll processes.

[0014] The inventors of the present invention thoroughly analyzed the structure of the cathode, taking into account the production in the roll-to-roll process and the electrical function in the wound electrolytic capacitor. The manufacturing process applies longitudinal stress to the cathode, so the cathode needs to have sufficient stability, especially sufficient tensile strength, to withstand the stress. In the wound electrolytic capacitor, the cathode needs to provide at least a conductive surface that provides capacitance. Furthermore, in order to provide sufficient capacitance, it is very suitable that the conductive surface is also surface-reinforced. In the conventional cathode, the entire cathode is made of aluminum, a similar metal, or an alloy, and the metal provides both tensile strength and electrical conductivity, so both functions are intertwined. However, this structure requires a certain minimum thickness. In view of this, the inventors separated the part of the electrical function from the part of the function that provides stability or tensile strength. The latter function is provided by the carrier substrate, while the electrical function is provided by the metal coating. Thus, the metal coating formed on the carrier substrate surface can provide the electrical conductivity and other electrical functions required for the coiled electrolytic capacitor, while the carrier substrate can prevent the electrode from cracking or splitting in the roll-to-roll process. The carrier substrate has a first metal coating on its first side, which may not provide an electrical function itself, the metal coating provides an electrical function. The carrier substrate may be non-metallic, non-conductive or insulating. In this case, the density of the non-metallic material may be lower than that of the metal, so that it is also possible to reduce the weight of the cathode and therefore the weight of the wound electrolytic capacitor.

[0015] The inventors have realized that by providing a carrier substrate, the electrical functional part, which is a metal coating, can be thinned to a thickness of 0.01 to 1 μm. Furthermore, the entire electrode can also have a thickness less than that of a conventional electrode. Alternatively, the combination of an electrode according to the first aspect with a separator, as will be explained in more detail below, can be thinner in a wound capacitor than a conventional electrode with a separator. In either case, the volumetric efficiency of the capacitor can be increased accordingly.

[0016] The cathode according to the invention can be thinner than conventional cathodes. This can, among other things, increase the volumetric efficiency. A thinner cathode allows the wound electrolytic capacitor to be constructed smaller while maintaining a constant capacitance. Alternatively, if it is possible to make one layer, such as the cathode, thinner, the area of ​​the layer in the wound capacitor coil can be increased. The free volume obtained by the reduction in thickness allows the area of ​​all components in the coil of the wound electrolytic capacitor to be increased. This area can be increased by providing the wound electrolytic capacitor coil with longer electrodes.

[0017] The metal coating preferably comprises aluminium. In particular, the metal coating is preferably made of aluminium. The metal coating may be composed of aluminium and compounds derived from aluminium such as aluminium oxides and hydroxides. Aluminium is highly conductive and can be advantageously processed by thin film techniques to form metal coatings in the thickness range of 0.01-1 μm. Aluminium can also facilitate surface strengthening or etching.

[0018] Furthermore, in the electrode, the carrier substrate preferably has a higher tensile strength than the first metal coating.

[0019] In particular, it is preferred that the material of the carrier substrate has a higher tensile strength along at least one spatial direction than the metal coating.

[0020] In particular, it is preferred that the tensile strength of the carrier substrate in the direction of winding, i.e. in the long extension direction (longitudinal direction) of the electrodes of the wound electrolytic capacitor, is higher than the tensile strength of the metallization, which allows the electrodes to be thinner than if they consisted purely or mainly of the material of the metallization.

[0021] Thus, in the case of an aluminum metallization on a carrier substrate that has a higher tensile strength than aluminum, the electrodes can be constructed thinner than in the case where the electrodes consist purely of aluminum, yet the thinner electrodes are still able to handle the tensile stresses of the roll-to-roll process.

[0022] According to a further aspect, the carrier substrate can have a second metallization on its second side. In particular, it is preferred that the carrier substrate has a second metallization formed on the second side of the carrier substrate.

[0023] In the case of insulating, non-conductive substrates that cannot be penetrated by the electrolyte of wound electrolytic capacitors, the second metal coating allows the capacitance to be utilized on both sides of the substrate, since the electrolyte can be in contact with the metal surface on both sides of the substrate, thereby maximizing the capacitance. This also allows both sides of the electrodes to be in contact with the electrolyte in a conventional wound electrolytic capacitor stack. Thus, the electrodes can completely replace conventional electrodes, and the electrodes, which are fully metallic, can also have an electrode-electrolyte interface on both sides.

[0024] Furthermore, the carrier substrate also provides the tensile strength to the second metal coating. Thus, in a configuration of a carrier substrate with a first and a second metal coating on both sides, the carrier substrate has the function of providing mechanical or tensile strength, while the electrical function is fulfilled by the first and the second metal coating. In particular, it is preferred that the carrier substrate has a higher tensile strength than the second metal coating. Furthermore, it is preferred that the materials of the first and the second metal coating are the same.

[0025] In particular, it is further preferred that the carrier substrate is a continuous or non-porous substrate, or a substrate that is not permeated by the electrolyte in wound electrolytic capacitors. A continuous or non-porous carrier substrate makes it possible to have a smooth metallization that is accessible by unsophisticated surface enhancement techniques.

[0026] It is particularly preferred that the carrier substrate comprises a polymer material.

[0027] The inventors of the present invention have found that by using a polymer material for the carrier substrate and two metal coatings on either side of the polymer substrate, the electrodes can have a thickness in the range of 4-7 μm while being able to handle the stresses of the roll-to-roll process. In particular, such electrodes can have less than half the size of conventional cathodes made of aluminum while functionally completely replacing the latter. Polymers as carrier substrate materials can offer excellent weight-saving benefits since both have a lower density than metals, allowing for thinner electrodes.

[0028] According to a further aspect, the carrier substrate can at least partially act as an electrolyte-containing or electrolyte-retaining separator for an electrolytic capacitor. Furthermore, the second side of the carrier substrate in this aspect is free of metal coating or remains free of metal coating.

[0029] This means that this embodiment relates to a configuration in which only one metal coating is present on a carrier substrate which can at least partially fulfill the role of an electrolyte-containing or electrolyte-retaining separator.

[0030] In conventional capacitor constructions, there is always a separator between the anode and cathode, and the separator itself has a required thickness due to electrotechnical requirements such as providing sufficient insulation and sufficient distance between the cathode and anode.

[0031] If the material of the carrier substrate is similar to the separator or can at least partially fulfill the role of the separator in a wound electrolytic capacitor, and is metallized on only one side, the electrolyte can penetrate or soak into the carrier substrate, thereby accessing the metallization from two sides. This allows for an easier production process, since only one side needs to be metallized, while a second anode / cathode gap can be formed, increasing the capacitance.

[0032] Furthermore, the inventors have found that the carrier substrate can at least partially replace the separator in the wound electrolytic capacitor configuration in terms of its volume or function. In particular, the thickness of the separator can be reduced because at least part of the separation function can be performed by the carrier substrate. For example, the thickness of the separator can be reduced to about the same extent as the thickness of the carrier substrate. As will be explained in more detail below, even a carrier substrate having a sufficient thickness to completely replace the separator is possible.

[0033] This means that in this embodiment, the sum of the carrier substrate, which can partially fulfill the role of a separator, and the separator (which may not even be present in some cases) can be thinner than the sum of a conventional electrode and a conventional separator.

[0034] It is particularly preferred that the carrier substrate can be at least partially permeated or immersed with the electrolyte, in particular that the material of the carrier substrate can be permeated or immersed with the electrolyte of the electrolytic capacitor, which has the advantages mentioned above.

[0035] In particular, to achieve this, the carrier substrate may be porous, for example, the carrier substrate may be sponge-like.

[0036] Alternatively, the carrier substrate may be a fibrous carrier substrate, which means that the material of the carrier substrate comprises fibers. The fibers may be natural or artificial fibers. Natural fibers are more preferred, since they are more easily wetted by the electrolyte. An example of a natural fiber that may be preferably used and included in the substrate is cellulose fiber, which shows an advantageous wetting behavior by the electrolyte.

[0037] If the carrier substrate is fibrous, it may be preferred that the fibers are interwoven so that a macroscopic interwoven superpattern is formed for the fibers. However, it is also possible that the fibers are nonwoven, which does not exclude the possibility that there may be some degree of order at the microscopic or mesoscopic level. In this case, the fibers may be loose, naturally attached, or may be compressed, matted, or felted. In the case of a substrate such as paper, it is most preferred to compress the substrate by calendering to increase its tensile strength. Thus, it is preferred that substrates such as paper are calendered. Alternatively, increased tensile strength may be provided by having a woven substrate. A textile may increase the tensile strength in all spatial directions. A nonwoven substrate may be advantageous over a woven substrate in that it is more easily saturated with the electrolyte.

[0038] In particular, the carrier substrate may be a separator material, which is particularly preferably paper or comprises paper.

[0039] The fibrous or porous materials described above may further provide higher tensile strength than metal coatings.

[0040] Thereby, a double role can be fulfilled: firstly, the carrier substrate can carry the metal coating and secondly, at least partially, the role of a separator.

[0041] According to another embodiment, the carrier substrate can have a thickness of less than 15 μm. Furthermore, the metal coating may have a thickness in the range of 0.01 to 1 μm. It is even more preferred that the entire electrode has a thickness of less than 15 μm.

[0042] Additionally, the metal coating may be surface hardened to provide a resistance of at least 5 μF / cm 2 The metallization provides a surface capacitance of at least 20 μF / cm 2 It is even more preferred to provide a surface capacitance of

[0043] Surface strengthening can be achieved by various methods. This can include the application of a metal coating to the rough surface of the carrier substrate, which also roughens the thin metal coating. Furthermore, post-deposition treatments such as lithography, or etching, or electrochemical etching may be applied.

[0044] The surface enhancement of the electrode, especially when applied as a cathode in a wound electrolytic capacitor, can improve the capacitance of the wound electrolytic capacitor.

[0045] According to a further embodiment, the carrier substrate provides a tensile strength to the electrodes of at least 10 N / cm, such tensile strength allowing handling in a roll-to-roll process.

[0046] According to further aspects, the metal coating may comprise multiple layers. As described below, several methods for forming a metal coating on a carrier substrate may result in a very thin metal film as the metal coating.

[0047] Providing multiple layers, one on top of the previous one, is advantageous since in this way the desired thickness can be reached, which may allow for example improved surface reinforcement by post-treatment, since a sufficient thickness allows for deeper three-dimensional structures.

[0048] In particular, when the metal coating is layered or comprises multiple layers, it is preferred that the individual layers of the metal coating are ribbon- or strip-like, which can then be arranged one on top of the other in a mesh pattern, forming ridges and depressions, thereby increasing the surface area of ​​the metal coating.

[0049] According to another aspect, a wound electrolytic capacitor is described. The capacitor according to this aspect comprises an anode and a cathode, the cathode having the properties of an electrode metallized on only one side of a carrier substrate, the carrier substrate possibly partially playing the role of a separator. All preferred aspects described for this type of electrode or cathode are also applicable in the case of this wound electrolytic capacitor.

[0050] In this wound electrolytic capacitor, a separator is disposed between a metallized first side of a carrier substrate and a side of the anode facing the metallized first side of the carrier substrate, and the first separator and the carrier substrate, which may at least partially act as an electrolyte-containing or electrolyte-retaining separator, are immersed in an electrolyte.

[0051] In this configuration, the carrier substrate may at least partially act as a separator for the gap between the cathode and the anode that does not have a first separator, in other words, the carrier substrate may at least partially function as a separator between the inside of the first metallization and the side of the anode that faces the second side of the carrier substrate.

[0052] It may be preferred that the gap formed between the non-metallized second side of the carrier substrate and the side of the anode facing this second side of the carrier substrate is free of an additional separator.

[0053] In this case, the role of the separator is completely fulfilled by the carrier substrate.

[0054] However, according to another alternative embodiment, an additional second separator can be arranged between the second side of the carrier substrate, which is the non-metallized side, and the side of the anode facing the second side of the carrier substrate.

[0055] In this case it is possible to have a thinner second separator, as in this case the substrate cannot at least partially fulfill the role of the separator.

[0056] Thus, in such configurations, and even in configurations without a second separator, it is possible to increase the volumetric efficiency of a wound electrolytic capacitor by having a smaller combined thickness of the cathode and optional second separator, with the caveat that the optional second separator can be replaced, either completely or at least in part, by the cathode.

[0057] According to another aspect, a wound electrolytic capacitor is described having an anode and a cathode, which is an electrode having a carrier substrate metallized on both sides, and two separators are disposed in the coil of the wound electrolytic capacitor between the metallized sides of the cathode and the side of the anode facing the side of the cathode.

[0058] As noted above, the cathode can be thinner than conventional cathodes because the tensile strength provided by the carrier substrate can be thinner than that provided by a portion of a conventional electrode comprised solely of metal.

[0059] It is possible to contact the anode or cathode in a wound electrolytic capacitor by means of a lead tab which can be assembled on the surface of the electrode and wound into the wound electrolytic capacitor. In particular, the lead tab can be applied to a cathode which is metallized on both sides. It is technically simple to apply the lead tab if the substrate is homogeneous and solid. For this reason, it is particularly suitable for the application of the lead tab that the substrate is non-porous or non-fibrous. This is preferably realized for substrates which are metallized on both sides and therefore do not need to be fibrous or porous. The lead tab may be applied to the electrode, for example, by cold pressing.

[0060] In the case of a cathode, where the carrier substrate can at least partially act as a separator, the application of lead tabs is technically more difficult, since the morphology of the carrier substrate material is often more irregular. In this case in particular, but also in the case of a cathode metallized on both sides, it is more preferable to have the following configuration: In a wound electrolytic capacitor, it is preferable that at least a part of the cathode extends the anode towards one side of the capacitor coil, and that the extended part of the cathode has a metal cover that covers at least a part of the side and allows external contact.

[0061] If the cathode extends towards the bottom or top side of the capacitor coil, this side can be covered with a metal cover to which the extended winding of the cathode is connected. In this way, the equivalent series resistance (ESR) can be reduced, since at least some of the individual windings are connected in parallel by the metal cover. In particular, this type of connection can be more advantageous than lead tabs.

[0062] In a wound electrolytic capacitor configuration, the metal cover can provide the external contact for the cathode, or negative terminal. External contact for the anode can be provided via a lead tab.

[0063] In all the above wound electrolytic capacitors having the above defined electrode as cathode, the reduction in thickness allows the lengthening of all components of the wound capacitor, i.e. the cathode, anode and separator, since in a capacitor of fixed dimensions the cathode requires less volume in the coil. For example, a thinner cathode may allow the anode to be increased in length by 7% to 20%, and similarly for the other components, resulting in a 7% to 15% increase in capacitance compared to a capacitor of conventional volume or external dimensions.

[0064] In another aspect, the use of such an electrode as described above as a cathode in a wound electrolytic capacitor is described. The advantageous properties and benefits cited for the electrode and the details given for the wound electrolytic capacitor also apply to the use of the electrode as a cathode in a wound electrolytic capacitor.

[0065] Further described is a process for forming electrodes for wound electrolytic capacitors in a roll-to-roll process, in which a carrier substrate is continuously wound from a first roll, a metal coating is continuously applied to at least a portion of a first side of the carrier substrate, and the metal coated portion of the carrier substrate is continuously wound onto a second roll.

[0066] The carrier substrate may have the properties defined above, in particular it may provide sufficient tensile strength for the electrodes to be processed in a roll-to-roll process, which is compatible with the present roll-to-roll process, but also with roll-to-roll to form wound electrolytic capacitor coils.

[0067] Additionally, a second metallization may be applied to a second side of the carrier substrate.

[0068] In this process, the metal coating may be applied to the carrier substrate, i.e., the first side and / or the second side, by physical vapor deposition, atomic layer deposition, chemical vapor deposition, or galvanic electrochemical deposition. Physical vapor deposition may be, for example, thermal evaporation, electron beam evaporation, sputtering, or pulsed laser deposition. These techniques can produce thin or ultrathin metal coatings with thicknesses ranging from 0.01 to 1 μm.

[0069] According to a further aspect, the metallization after formation may be post-treated by plasma etching, electrolytic etching, or lithography to achieve the surface enhancements described above.

[0070] According to a further aspect, in this process the metallization may be formed as a layer in a subsequent roll-to-roll process step or in one roll-to-roll process step where metallization sub-layers are applied from several sources.

[0071] Having a multi-layer metallization can have the advantages mentioned above.

[0072] In particular, in a subsequent deposition step, or in a subsequent roll-to-roll step, or in one roll-to-roll step using several deposition sources, partial layers may be formed that have the form of ribbons or strips and that can be applied so that a net-like pattern is formed.

[0073] Thereby the surface can be strengthened, which means that a larger surface area can be created.

[0074] Further described is a process for forming a capacitor comprising the above electrodes, i.e. the process described above, which comprises winding the electrodes in a roll-to-roll process, the negative electrode being an electrode as described above with the anode and a separator as described for the above embodiment, further comprising impregnation or immersion with an electrolyte.

[0075] Furthermore, a lead tab, or several lead tabs, may be applied to the cathode and / or anode, for example by welding. In particular, this may be appropriate for a cathode with a double-sided metal coating. Furthermore, in addition to this, or alternatively, it is also possible to provide a metal cover for a wound electrolytic capacitor with a cathode extending towards one side of the wound electrolytic capacitor. For example, the metal cover may be applied by metal spray, which may be a thermal spray process. Examples of thermal spray processes or thermal spray techniques are arc, flame, plasma, high velocity oxygen fuel, or other spray layer deposition methods. Alternatively, a combination of these may be applied to one or several metals to form a metal cover. [Brief description of the drawings]

[0076] In the following, the invention will be described in more detail by means of examples of embodiments and with reference to figures. The figures contain both embodiments and process-related information. It should be noted that in the schematic drawings or representations, the components are not shown to scale. In these, the components may be shown distorted in size, length or length ratios. Such ratios may not be taken from the schematic drawings. [Figure 1] FIG. 1 is an electron microscope image of a conventionally etched aluminum cathode. [Diagram 2] FIG. 2 is an electron microscope image of an alternating current (AC current) etched aluminum cathode. [Diagram 3] FIG. 3 is a cross-sectional electron image of a conventional all-metal electrode. [Figure 4] FIG. 4 is a schematic diagram of a first embodiment of a cathode. [Diagram 5] FIG. 5 is a schematic diagram of a second embodiment of the cathode. [Figure 6] FIG. 6 is a schematic diagram of a third embodiment of the cathode. [Figure 7] FIG. 7 is a schematic diagram of a first embodiment of a process for forming a cathode. [Figure 8] FIG. 8 illustrates a second embodiment of a process for forming a cathode. [Figure 9] FIG. 9 is a diagram showing a wound type electrolytic capacitor. [Figure 10] FIG. 10 is a schematic diagram of a first embodiment for stacking in a wound electrolytic capacitor. [Figure 11] FIG. 11 is a schematic diagram of a second embodiment of a stack in a wound electrolytic capacitor.

[0077] Figure 1 shows a secondary electron image recorded by a scanning electron microscope of a common cathode made of alumina and etched with a crude electrochemical etching process. Surface enhancement can be achieved in this way. As can be seen in Figure 1, the three-dimensional structure of the surface enhancement or surface is irregular.

[0078] Similar etching can also be applied to the electrodes or cathodes according to the invention.

[0079] Figure 2 shows a secondary electron image recorded with a scanning electron microscope of an aluminum-based cathode foil etched with a sophisticated alternating current (AC current) etching method, which allows the production of more regular, ordered structures than the less sophisticated electrochemical etching shown in Figure 1.

[0080] Thus, as can be seen from FIG. 2, AC etching results in a more regular surface structure, which leads to better efficiency in terms of capacitance and also in terms of capacitance gain versus weight loss.

[0081] In Figure 3, a cross-sectional electron microscope image of a conventional cathode is shown. It is revealed that the conventional cathode is relatively thick, with a thickness of about 40 μm. Conventionally, the thickness of such a cathode is in the range of 15 to 60 μm. In particular, the roll-to-roll process used in the production of wound electrolytic capacitors needs to meet a certain tensile strength of at least about 10 N / cm. To achieve this, the unetched part (the part sandwiched by the two brighter areas in Figure 3) needs to be not too thin.

[0082] The inventors of the present invention have recognized that by separating the parts that provide mechanical strength from the technically relevant parts that are metal or conductive surfaces, it is possible to reduce the thickness of the electrodes in general, and the thickness of the cathode in particular, thereby reducing the volume of the wound electrolytic capacitor, or increasing the length or area of ​​all the components wound in the wound electrolytic capacitor, thereby increasing the capacitance for a given volume.

[0083] FIG. 4 shows a schematic diagram of a first embodiment of a cathode 1 as an example for an electrode. The cathode 1 has the form of a film or is a cathode film. The cathode 1 comprises a carrier substrate 2. The carrier substrate 2 is non-conductive or non-metallic. A metal coating 3 is assembled on a first surface of the carrier substrate 2. The metal coating 3 can be formed on the first surface of the substrate 2. The cathode 1 is suitable for being incorporated into a wound electrolytic capacitor.

[0084] It should be noted that the principles described here and below for the cathode may also be applied to the anode of a wound electrolytic capacitor, where technically applicable.

[0085] The carrier substrate 2 has a higher tensile strength than the metal coating 3. In particular, the carrier substrate 2 is capable of providing the electrode with at least a tensile strength of 10 N / cm.

[0086] The metal coating is a thin metal film that can be applied by a variety of techniques, as described below. The metal coating has a resistivity of at least 5 μF / cm 2 The metal coating 3 may be surface enhanced to provide a specific capacitance of 0.01-1 μm. The metal coating may comprise or consist of any suitable metal or alloy. However, most suitably the metal coating comprises aluminium. Suitably the electrodes have aluminium as a main component. The electrodes may be constructed of aluminium.

[0087] The metal coating 3 can perform the electrical function of a conventional metal electrode, however, because stability and tensile strength are provided by the carrier substrate 2, the metal coating 3 can be much thinner than a conventional electrode.

[0088] In particular, the carrier substrate 2 may be a polymer substrate with a thickness of less than 15 μm, in which case a second metallization is preferred, as described below.

[0089] Alternatively, the carrier substrate 2 may at least partially play the role of an electrolyte-containing or electrolyte-retaining separator for an electrolytic capacitor. In particular, the carrier substrate 2 may be capable of being permeated or immersed by the electrolyte of the electrolytic capacitor. To that end, the carrier substrate 2 may be porous or fibrous. The fibers may be of any nature, but cellulose fibers are most suitable. In particular, the substrate may be a paper-like material similar to that of the separator of the electrolytic capacitor. Alternatively, woven or non-woven fibers may also be used. With these properties, the cathode 2 shown in FIG. 4 is most suitable when the carrier substrate 2 only has a first metallization 3 and no further metallizations. In this case, the thickness of the carrier substrate may be less than 15 μm. However, if the carrier substrate is intended to completely replace the separator in a wound electrolytic capacitor, the thickness may be greater.

[0090] In Fig. 5 a schematic diagram of a second embodiment of a cathode 1 is shown. The cathode 1 may have the same properties as described for the first embodiment shown in Fig. 4. However, in the case of the cathode according to Fig. 5 the carrier substrate 2 is not permeable by the electrolyte. Most preferably the carrier substrate 2 comprises or consists of a polymer. Examples of suitable polymers are polypropylene (PP) or polyethylene terephthalate (PET). In the case of the second embodiment a first metallization 3 and a second metallization 4 are formed on the carrier substrate 2. The metallizations 3, 4 may be identical with respect to their properties and structure.

[0091] In the case of an impermeable substrate, the cathode 1 can completely replace all the electrical functions of a conventional cathode.

[0092] In this case, in particular, the total thickness may be less than 16 μm. In particular, the carrier substrate may have a thickness of less than 15 μm and the metal coatings 3, 4 each have a thickness of 0.01 to 1 μm. It is more preferred that the electrodes have a thickness of less than 10 μm. The thickness of the polymer substrate may be in the range of 1 to 7 μm, while it is even more preferred that the metal coatings have the thicknesses defined above. Overall, this allows the cathode to have a thickness in the range of 3 to 7 μm, which is most preferred. Thus, with the electrode of FIG. 4, a considerable thickness reduction can be achieved compared to conventional cathodes. Thus, the thickness can be reduced by more than 50% compared to conventional cathodes.

[0093] In Fig. 6 a schematic diagram of a third embodiment of the cathode 1 is shown. The cathode 1 of the third embodiment is identical in its properties to the cathode of the second embodiment, as shown in Fig. 5. However, the metallizations 3, 4 each comprise a sub-layer 3', 4' respectively. The metallizations are layered.

[0094] By having multiple layers, it is possible to achieve the desired film thickness by various thin film deposition techniques by depositing some layers on top of others, thus forming the desired thickness for post-deposition processing of the metallization.

[0095] It is also possible to have discontinuous layers, for example layers in the form of ribbons or strips arranged rectangularly relative to one another to form a mesh pattern, which creates depressions and protrusions in the surface, thereby enhancing the active surface.

[0096] In FIG. 7, a schematic diagram of a first embodiment of a roll-to-roll process is shown. In a roll-to-roll process for forming cathodes of wound electrolytic capacitors, a carrier substrate 2 is provided on a first roll 5. The carrier substrate 2 is continuously unwound from the first roll 5. The carrier substrate 2 may pass one or more guide rolls 6 that guide or redirect the carrier substrate 2. The carrier substrate 2 is continuously unwound onto a second roll 9. Between the first roll 5 and the second roll 9, the carrier substrate 2 is metallized on at least one side by a first metallizer 7. In particular, the metallizer 7 may be any device that is capable of applying or forming a first metallization on the first side of the carrier substrate 2. In particular, the metallization is preferably performed by a physical vapor deposition technique (PVD technique), such as thermal evaporation, electron beam evaporation, sputtering or pulsed laser deposition. Alternatively, atomic layer deposition or chemical vapor deposition can also be applied. The metallizer 7 can be located at any technically suitable position. In the depiction of FIG. 7, the metallizer 7 is positioned facing the guide roll 6 , which ensures that the passing film is in a stable position relative to the metallizer 7 .

[0097] With this configuration in Figure 7 it is possible to coat one side of the carrier substrate 2 in one run to achieve a configuration as shown in Figure 4. In particular this is suitable for a cathode which can at least partially play the role of an electrolyte-containing or electrolyte-retaining separator for an electrolytic capacitor.

[0098] In the case of a polymer or similar substrate, a second metallization can be applied in a similar manner by metallizing the second side of the carrier substrate 2 in a second roll-to-roll process.

[0099] After the depicted roll-to-roll process, the metallization may be surface-reinforced, in particular by applying plasma etching, electrolytic etching, or lithography.

[0100] Alternatively, or in addition, multiple depositions of the metal coating can be performed on the surface to obtain a layered structure as shown in Figure 6. Thereby, partial layers, such as ribbon or strip-like shapes, can be applied in a net-like pattern to form a surface-reinforced metal coating.

[0101] FIG. 8 shows a schematic diagram of a second embodiment of a process for forming a cathode.

[0102] The principle is similar to that described for the first embodiment of the process shown in Fig. 7. In particular, the carrier substrate 2 is continuously unwound from a first roll 5 and continuously wound onto a second roll 9. Between the first roll 5 and the second roll 9 the carrier substrate passes through several guide rolls 6, which serve to expose two different sides of the carrier substrate 2 at different points.

[0103] The carrier substrate 2 first passes through a first metallizer 7 which metallizes a first side of the carrier substrate 2. After being re-guided by a number of guide rolls 6, the carrier substrate 2 passes through a second metallizer 8 which metallizes the other (second) side of the carrier substrate 2. Both the first and the second metallizer are positioned facing the guide rolls 6 for the reasons explained with respect to FIG.

[0104] Alternative configurations are possible in which the second metallizer is positioned such that no guiding by a guide roll is required, for example by positioning the second metallizer to face the second side of the carrier substrate 2.

[0105] This configuration allows the capacitor to be metallized on both sides in one roll-to-roll process to form a structure as shown in FIG.

[0106] It is also possible to form a layered metal coating for one side in one configuration by using several evaporators, or by having several roll-to-roll processes in sequence, or by having a special metallizer.

[0107] 9 shows a wound electrolytic capacitor 10 with all the coiled components (not visible) inside the capacitor. The wound electrolytic capacitor 10 includes a side cover 11 that may protect the internal coil from physical impact.

[0108] Furthermore, a metal cover 13 is provided at the bottom of the wound electrolytic capacitor 10. In this particular case, the metal cover 13 may allow external contact of the cathode, as described below. The anode may be contacted via several lead tabs 12 included in the wound capacitor coil. For example, the metal cover may be applied by metal spray, which may be a thermal spray process. Examples of thermal spray processes or thermal spray techniques are arc, flame, plasma, high velocity oxygen fuel, or other spray layer deposition methods. Alternatively, a combination of these may be applied to one or several metals to form the metal cover.

[0109] In FIG. 10, a schematic diagram of a capacitor coil of a wound electrolytic capacitor is shown. The coil is partially unfolded to show the stacking of layers. The wound electrolytic capacitor comprises an anode 16 in the form of an anode film and a cathode 1. The anode 16 may be a conventional anode with a thickness in the range of 110-130 μm. The cathode 1 may be a cathode with a carrier substrate which may have the above mentioned characteristics and in particular may at least partially play the role of an electrolyte-containing or electrolyte-retaining separator. In particular, the explanation as given for FIG. 4 may be applicable to the cathode 1. Moreover, as can be seen from the enlarged view on the right, the cathode 1 is metallized on only one side (the first side) of the carrier substrate 2. The first metallization 3 faces inwards and thereby faces the surface towards one side of the anode 16. Between this side of the anode 16 and the first side of the substrate 2 on which the metallization 3 lies, a first separator 14 is integrated. The first separator 14 may have a thickness of 30 to 50 μm. The gap between the first separator 14 electrically and spatially separates the cathode 1 and the anode 16. Furthermore, the anode 16 is contacted via a lead tab 12 wound around the wound electrolytic capacitor.

[0110] Both the first separator 14 and the carrier substrate 2, when assembled into a capacitor, are saturated or wetted by the electrolyte of the electrolytic capacitor.

[0111] In this depiction, no additional separator is provided in the gap between the second side of the carrier substrate 2, which is the side without metal coating, and the side of the anode 16 facing this side in the wound electrolytic capacitor coil. In this case, the carrier substrate 2 can fully fulfill the role of the second separator. In particular, the carrier substrate 2 can contain or be impregnated with an electrolyte. This allows the diffusion of the electrolyte. This spatially and electrically separates the first metal coating 3 from the anode 16 in the direction of the second side of the carrier substrate 2.

[0112] However, alternatively, the second separator may also be arranged in a similar manner, as described with respect to Fig. 11. However, in the case of the depiction of Fig. 10, it would be possible to reduce the thickness of the second separator to approximately the thickness of the carrier substrate, due to the fact that the carrier substrate may at least partially fulfill the role of the separator.

[0113] The total thickness of the combination of the cathode 1 and the potential second separator (not present at all in FIG. 10) can be less than the sum of the thicknesses of the conventional cathode and the conventional separator adjacent to it. In the case of a conventional separator, the cathode may have a thickness of more than 15 μm and the separator may have a thickness in the range of more than 30 μm. In the present invention, the entire cathode with the substrate, which can at least partially fulfill the role of the separator, can have a thickness of 3 to 7 μm. In this case, the additional separator (not the first separator) may have a thickness in the range of 15 to 25 μm. Thus, a thickness reduction of at least 28% can be achieved.

[0114] Furthermore, the cathode 1 has a width that extends towards the side that is the bottom of the condenser coil. The width is extended relative to the size of the anode 16 in the coil. At the bottom (side of the condenser coil) a metal cover 13 is applied that contacts each individual winding of the cathode 1. Thereby, external contact of the cathode is possible and a low equivalent series resistance (ESR) is achieved due to the parallel circuit formed by the metallization. The contact of the anode is carried out via a lead tab.

[0115] Alternatively, it is possible to provide a lead tab for the cathode, but this is less preferred for the reasons discussed above, plus it is technically difficult to attach a lead tab onto the thin metal film when the thin metal film is provided on a porous or fibrous substrate.

[0116] A schematic diagram of a second embodiment of a coil of a wound electrolytic capacitor is shown in Fig. 11. In general, the characteristics of the second coil may be identical to the first coil shown in Fig. 10. However, in this case the cathode 1 is a cathode with two metal coatings 3, 4 on both sides of the carrier substrate 2, as shown in Fig. 5.

[0117] The cathode 1 may have a thickness in the range of 3 to 7 μm, which is at least half that of a conventional aluminum cathode.

[0118] The anode 16 may have a thickness in the range of 110 to 130 μm. Furthermore, again, a first separator 14 is assembled between a first side of the cathode 1 and a side of the anode 16 facing this first side of the cathode. Furthermore, a second separator 15 is assembled between a second side of the cathode and the other side of the anode facing the second side of the cathode. Both separators may have a thickness in the range of 30 to 50 μm.

[0119] Overall, the above-mentioned thickness reductions allow the anode, cathode, and separator lengths to be increased by 7-20% compared to conventional wound electrolytic capacitors with pure aluminum cathodes, resulting in a 7-15% increase in capacitance.

[0120] The external electrical contact can be as described above for Figure 10. However, it should be noted that a polymer foil with metallization on both sides is more suitable if the cathode 1 is also provided with a lead tab for external electrical contact.

[0121] However, this configuration can still provide a reduction in equivalent series resistance due to contact of the cathode through the metal cover 13.

[0122] Tables 1 and 2 show an experimental series of 10 capacitors (Cap1-Cap10) with size 30x60mm according to the embodiment of Figure 11. In particular, the capacitors have a double-sided metallized polymer film as the cathode.

[0123] As can be seen from Table 1, at a frequency of 100 Hz, capacitances of 640 to about 765 μF could be achieved. At a frequency of 100 Hz, the equivalent series resistance was between 590 and 670 mΩ. The impedance measured at this frequency was between 2179 and 2557 mΩ.

[0124] Similar values ​​were achieved at a frequency of 120 Hz. In particular, the capacitance was between 634 and 746 μF. The equivalent series resistance was between 567 and 634 mΩ. Furthermore, the impedance was between 1867 and 2177 mΩ.

[0125] 10 4 At 350 Hz, the capacitance is in the range of >305 μF to 329 μF. The equivalent series resistance is between 247 mΩ and 266 mΩ. The impedance is between 252 mΩ and 271 mΩ.

[0126] 10 5 At Hz, the capacitance is between 103 μF and 119 μF. The equivalent series resistance is between 234 and 252 mΩ. The impedance is between 235 and 252 mΩ.

[0127] From the frequency dependence in Table 1, the extinction coefficient tan δ is calculated to be between 29 and 34. [Table 1]

[0128] Furthermore, in Table 2, it can be seen that the self-discharge is good. In particular, the current value after 1 minute of charge loss due to leakage current (LC 1 min The leakage current (LC) after 2 minutes is shown to be in the range of 218-260 μA. 2 min ) was between 116 and 150 μA, and the leakage current (LC 5 min ) is between 61 and 80 μA.

[0129] Furthermore, Figure 2 shows that using a cathode with a polymer carrier substrate, it is possible to form a fairly light wound electrolytic capacitor with a size of 30 x 60 mm. The weight of the electrolytic capacitor was between 76.9 and 77.5 g. In particular, using a double-sided metallized polymer film cathode with a size of 30 x 60 mm, a weight of less than 77.5 g can be achieved. [Table 2] [Explanation of symbols]

[0130] 1 cathode 2 Carrier Board 3 First Metal Coating 4 Second Metal Coating 5. First Roll 6 Guide Roll 7. First Metallizer 8 Second Metallizer 9. Second Roll 10 Turn Electrolytic Capacitor 11 Side cover 12 Lead tab 13 Metal cover 14 First separator 15 Second separator 16 Anode

Claims

1. An electrode for an electrolytic capacitor (10), comprising a carrier substrate (2) and a first metallization (3) formed on a first side of the carrier substrate (2).

2. The electrode according to claim 1 , wherein the carrier substrate (2) has a higher tensile strength than the metal coating (3).

3. 3. The electrode according to claim 1 or 2, wherein the carrier substrate (2) has a second metallization (4) formed on a second side of the carrier substrate (2).

4. The electrode according to claim 3 , wherein the carrier substrate (2) comprises a polymer material.

5. 3. The electrode according to claim 1 or 2, wherein the carrier substrate (2) is capable of at least partially fulfilling the role of an electrolyte-containing or electrolyte-retaining separator for an electrolytic capacitor, the second side of the carrier substrate (2) being free of a metal coating.

6. 6. The electrode according to claim 5, wherein the carrier substrate (2) is capable of being permeated or immersed with an electrolyte of an electrolytic capacitor.

7. 7. The electrode according to claim 5 or 6, wherein the carrier substrate (2) is porous.

8. 7. The electrode according to claim 5 or 6, wherein the carrier substrate (2) is a fibrous carrier substrate (2).

9. The electrode according to claim 8, wherein the carrier substrate (2) comprises cellulose fibres.

10. Electrode according to any one of the preceding claims, wherein the carrier substrate (2) has a thickness of less than 15 μm and the metal coating (3) has a thickness of 0.01 to 1 μm.

11. The metal coating (2) is surface-hardened, so that it has a resistance of at least 5 μF / cm ２ 11. An electrode according to any one of claims 1 to 10, which provides a specific capacitance of

12. The electrode according to any one of the preceding claims, wherein the carrier substrate (2) provides the electrode with a tensile strength of at least 10 N / cm.

13. The electrode according to any one of the preceding claims, wherein the metal coating (3) comprises a plurality of layers.

14. 14. The electrode according to claim 13, wherein the layers of the metal coating (3) are ribbons, the layers being arranged such that a mesh pattern is formed by the ribbons.

15. A wound electrolytic capacitor (10) comprising an anode (16), a cathode (1) which is the electrode according to any one of claims 5 to 9, and a first separator (14), the first separator (14) is disposed between the metallized first side of the carrier substrate (2) and a side of the anode (16) facing the metallized first side of the carrier substrate (2); A wound electrolytic capacitor (10), wherein the first separator (14) and the carrier substrate (2) are immersed in the electrolyte.

16. 16. The wound electrolytic capacitor (10) of claim 15, wherein no additional separator is provided in a gap formed by the second side of the carrier substrate (2) and a side of the anode (16) facing the second side of the carrier substrate (2).

17. 16. The wound electrolytic capacitor (10) of claim 15, wherein an additional second separator (15) is disposed between the second side of the carrier substrate (2) and the side of the anode (16) facing the second side of the carrier substrate (2).

18. A wound electrolytic capacitor (10) comprising an anode (16), a cathode (1) which is the electrode according to claim 3 or 4, and two separators (14, 15), A wound electrolytic capacitor (10), wherein the two separators (14, 15) are disposed between both metallized sides of the cathode (1) and the sides of the anode (16) facing these sides of the cathode (1).

19. 19. The wound electrolytic capacitor (10) of any one of claims 15 to 18, wherein at least a portion of the cathode (1) extends the anode (16) towards one side of the capacitor coil, the extended portion of the cathode (1) having a metal cover (13) covering at least a part of this side to allow external contact.

20. 1. A process for forming an electrode for a wound electrolytic capacitor in a roll-to-roll process, comprising: A carrier substrate (2) is continuously unwound from a first roll (5), A metal coating is continuously applied to at least a portion of a first side of the carrier substrate (2), A process in which the metallized portion of the carrier substrate (2) is continuously wound up onto a second roll (9).

Images