Anode lead tab and electrolytic capacitor

Abstract

The present invention relates to an anode lead tab (7) configured to externally contact an anode foil (3) in an electrolytic capacitor (1), the anode lead tab (7) providing a roughened surface that protects the anode lead tab (7) from surface dissolution.

Description

[Technical Field]

[0001] The present invention relates to an anode lead tab, an electrolytic capacitor having an anode lead tab, and a method for manufacturing the anode lead tab. [Background technology]

[0002] The lifespan of aluminum electrolytic capacitors is short due to the limited purity of the raw materials.

[0003] One common failure mode is electrochemical corrosion of the capacitor's anode lead tab, resulting in the lead tab's destruction.

[0004] Electrochemical corrosion of the anode lead tab is caused by halogen ions, which initiate an electrochemical reaction with the aluminum anode lead tab material. The most common halogen is Cl, which is a natural impurity in almost all raw materials. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] German Patent Application No. 102016125733 Summary of the Invention [Problem to be solved by the invention]

[0006] German Patent Application No. DE102016125733A1 discloses an oxide layer that protects aluminum anodes from environmental influences.

[0007] However, voids and cracks in the oxide layer are inevitable.

[0008] One object of the present invention is to provide an improved anode lead tab and an improved electrolytic capacitor. [Means for solving the problem]

[0009] The present invention provides an anode lead tab configured to externally contact an anode foil in an electrolytic capacitor, the anode lead tab being provided with a roughened surface that protects the anode lead tab from surface dissolution.

[0010] The electrolytic capacitor according to the present invention is a capacitor having a liquid electrolyte, an anode foil, a cathode foil, a separator between the anode foil and the cathode foil, and tabs that electrically connect the anode foil and the cathode foil to external contacts.

[0011] In particular, aluminum electrolytic capacitors are polarized capacitors in which the anode is made of aluminum, on which an insulating oxide layer is formed by anodization. The oxide layer functions as the dielectric of the aluminum electrolytic capacitor. A liquid electrolyte covers the surface of the oxide layer and, in principle, serves as the capacitor's second electrode, making electrical contact with the cathode foil. A separator is placed between the anode and cathode foil. The separator may comprise a paper sheet impregnated with the liquid electrolyte.

[0012] The aluminum electrolytic capacitor may be configured as a hybrid polymer electrolytic capacitor, which is an electrolytic capacitor having a liquid electrolyte and a solid electrolyte of conductive polymer particles. The polymer may cover the anode foil, the cathode foil, the separator, and the tabs that electrically connect the anode and cathode foils.

[0013] The anode lead tab is a conductive lead tab that electrically and mechanically connects the anode foil of the electrolytic capacitor to an external contact.

[0014] The anode lead tab may be configured as a flexible metal strip with one side secured to the anode foil and the other side secured to an external contact.

[0015] The metal strip may comprise a conductive metal, preferably aluminum (Al). The metal strip may comprise a metal foil, preferably aluminum foil.

[0016] The external contact may be configured as the bottom or cover of a can that contains the electrolytic capacitor. In one embodiment, the can can contain the capacitor and liquid electrolyte.

[0017] The external contact may be constructed as a separate element, or preferably, the external contact may be integrated into the cover or the bottom of the can.

[0018] The electrolytic capacitor may have a wound element.

[0019] The capacitor and wound element according to one embodiment includes an anode foil, a cathode foil, and a separator, which separates the anode and cathode foils.

[0020] The anode lead tab may be secured to the anode foil and external contact by clamping or welding, preferably by welding.

[0021] Electrolytic capacitors are impregnated with a liquid electrolyte.

[0022] The electrical lead tabs are in direct contact with the liquid electrolyte of the electrolytic capacitor.

[0023] Generally, in such capacitors, undesirable side reactions can occur between the liquid electrolyte and the electrical lead materials.

[0024] It is inevitable that the surfaces of electrical lead tabs contain at least a minimal amount of impurities. Liquid electrolytes also contain unavoidable impurities. Impurities can trigger or promote undesirable side reactions. Typical undesirable impurities include halogens such as chlorine (Cl), iodine (I), bromine (Br), and fluorine (F). In particular, the inclusion of a minimal source of Cl is inevitable.

[0025] Roughening the surface of the lead tab increases the surface area of ​​the lead tab. The impurities are more widely distributed over the increased surface area. This means that the spatial distance between single impurity particles increases, and therefore the impurity concentration per unit surface area decreases.

[0026] Impurities such as halogen ions and organic (halogen) compounds cause undesirable side reactions between the anode lead tab material and the liquid electrolyte surrounding the lead tab.

[0027] In the side reaction, the lead tab material is chemically converted into a soluble (halogen) salt that dissolves in the aqueous liquid electrolyte.

[0028] In the worst case, such side reactions can completely dissolve the anode lead tab. Wide distribution of such impurities prevents the formation of clusters of impurities that promote such side reactions.

[0029] In another embodiment, the anode lead tab is protected by an oxide layer, which, however, carries the risk of cracks or voids forming inside the layer, which provide hot spots for reactions and are favorable locations for side reactions to occur.

[0030] Side reactions can be suppressed by providing fewer impurity components at the hot spots. By roughening the surface and increasing the surface area, the concentration of impurities on the surface and in such hot spots can be reduced.

[0031] The liquid electrolyte contains inevitable impurities such as halogen ions and compounds such as Cl.

[0032] Accumulation of impurities at a single location on the electrical lead tab promotes side reactions.

[0033] Side reactions reduce the concentration of impurity components at the reaction sites where the side reactions occur, which leads to the diffusion of additional impurity compounds to the reaction sites.

[0034] Side reactions also result in an excess supply of positive cations at the reaction sites, which in turn leads to the diffusion of negatively charged anions, such as halide ions, to the reaction sites.

[0035] These effects promote side reactions and lead tab dissolution.

[0036] The roughened surface helps prevent the formation of hot spots of concentrated impurities on the surface of the lead tab, which can cause the undesirable effects described above.

[0037] In some embodiments, the specific surface area of ​​the roughened surface is at least 10 times greater than the specific surface area of ​​the smooth surface.

[0038] The aforementioned roughness prevents the undesirable accumulation of impurity elements on the surface of the electrical lead tabs, and the formation of concentrated clusters of impurity elements is further suppressed.

[0039] In one embodiment, the specific capacitance of the roughened surface is 3 μF / cm 2 In a preferred embodiment, the specific capacitance of the roughened surface is 5 μF / cm 2 More preferably, it is 30 μF / cm 2 That's all.

[0040] Specific capacitance is the electrical capacitance of a roughened surface relative to the area of ​​the surface projected onto a flat surface.

[0041] The specific capacity can be determined experimentally.

[0042] For example, an LCR meter (inductance L, capacitance C, resistance R) can be used to measure specific capacitance in a highly conductive electrolyte. Two tab samples are measured against each other.

[0043] A high specific capacity reduces the risk of undesired side reactions and electrical leakage or short circuit phenomena.

[0044] An additional advantage of the high surface anode lead tab is that its specific capacitance value approaches that of the normal anode foil capacitance value, thus reducing the risk of uneven current distribution between the surface of the anode foil and the surface of the anode lead tab, thereby minimizing the risk of a destructive short circuit between the anode lead tab and the cathode of the capacitor.

[0045] In one embodiment, the anode lead tab includes aluminum as a primary material.

[0046] Aluminum as a base metal has good electrical conductivity and is low in cost.

[0047] Furthermore, aluminum has good formability and good flexibility.

[0048] Therefore, flexible tabs of a desired shape can be easily manufactured, and high robustness against external mechanical shocks can be obtained.

[0049] In an air atmosphere, aluminum reacts with oxygen in the air to spontaneously form a protective aluminum oxide layer.

[0050] In some embodiments, the roughened surface is passivated with an oxide layer.

[0051] If the anode lead tab comprises aluminum, an oxide layer may form spontaneously due to reaction of the aluminum with oxygen in the air.

[0052] Additionally or alternatively, the oxide layer may be applied during the manufacture of the lead tab.

[0053] The oxide layer additionally protects the lead tab from external factors such as chemical surface reactions.

[0054] If undesirable cracks or voids occur within the oxide layer, a second protective measure is provided by surface roughening.

[0055] In one embodiment, the oxide layer has a thickness of at least 3 nm.

[0056] An oxide layer having such a thickness can minimize the risk of contact between the liquid electrolyte and the surface of the anode lead tab.

[0057] The present invention further provides an aluminum electrolytic capacitor having an anode lead tab according to any of the preceding embodiments.

[0058] In some embodiments, the aluminum electrolytic capacitor includes at least two or more anode lead tabs, at least one or all of which are configured according to any of the above-described embodiments.

[0059] The use of two or more anode lead tabs to connect the anode foil to an external contact or contacts allows the use of longer and wider anode foils. The use of multiple tabs also reduces the metal resistance of the wound element and allows current to be supplied to the wound element at multiple locations, thereby limiting the length the current must travel within the wound element.

[0060] The present invention further provides a method for manufacturing an anode lead tab that provides a roughened surface.

[0061] This may be configured according to any of the embodiments previously described.

[0062] The present manufacturing method includes at least the following steps.

[0063] In a first step, an anode lead tab having a smooth surface is provided.

[0064] In the second step, 3 μF / cm 2 The smooth surface is roughened by chemical etching, electrochemical etching, mechanical treatment, plasma treatment, laser treatment, or a combination of the above processes until the above specific capacitance is achieved.

[0065] The specific capacitance corresponds directly to the surface area and therefore to the surface roughness of the surface of the anode lead tab.

[0066] Hereinafter, embodiments of the present invention will be described in more detail with reference to the accompanying drawings. In the drawings, similar or apparently identical elements are represented by the same reference numerals. The drawings and proportions therein are not to scale. The present invention is not limited to the following embodiments. [Brief explanation of the drawings]

[0067] [Figure 1] 1A and 1B are diagrams illustrating a first embodiment of a wound element of an electrolytic capacitor. [Figure 2] FIG. 1 shows a photograph of a modern smooth lead tab surface. [Figure 3] 2 and 3 are diagrams showing the roughened lead tab surface of the present invention.The photographs in Figures 2 and 3 were taken with an SEM (scanning electron microscope). DETAILED DESCRIPTION OF THE INVENTION

[0068] FIG. 1 shows a diagram of a first embodiment of a wound element of an electrolytic capacitor 1.

[0069] The winding element 2 has, for example, a diameter of more than 10 mm and a height of more than 12 mm.

[0070] The wound element 2 may be housed in a cylindrical can, which may have a bottom and walls and may be covered by a cap or cover (not shown in Figure 1).

[0071] The wound element 2 includes an anode foil 3, a cathode foil 4, and a separator 5 wound around a common shaft. The separator 5 is disposed between the anode foil 3 and the cathode foil 4. The wound element 2 also includes another separator, which is also disposed between the anode foil 3 and the cathode foil 4, but is not shown in FIG. 1 for simplicity. In particular, 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 shaft. The wound element 2 may be impregnated with an electrolyte (standard aluminum electrolytic capacitor) or with a polymer and working electrolyte (hybrid polymer capacitor).

[0072] The capacitor 1 further comprises a liquid electrolyte 6 .

[0073] The anode foil 3 includes an aluminum foil, the surface of which may be roughened by, for example, etching.

[0074] The anode foil 3 has an aluminum foil with an oxide layer on its surface, which is formed by the self-oxidation or oxidation process.

[0075] The cathode foil 4 also includes an aluminum foil, the surface of which may be roughened by etching, and a dielectric oxide film formed on the surface by autoxidation or oxidation, so that the cathode foil 4 also includes an aluminum foil having an oxide layer on its surface.

[0076] Each of the separators 5 is an impregnable paper.

[0077] The common axis about which the winding element 2 is wound defines the axial direction.

[0078] The winding element 2 further has tabs 7 and 8, which are used for electrical contact with the winding element 2. The winding element 2 has two anode lead tabs 7, both of which are connected to the anode foil 3. The anode lead tab 7 connected to the anode foil 3 extends in the positive axial direction.

[0079] Furthermore, the wound element 2 has two cathode lead tabs 8, which are connected to the cathode foils 4. The cathode lead tabs 8 connected to the cathode foils 4 extend in the negative axial direction, i.e., in the opposite direction to the anode lead tab 7 connected to the anode foil 3, or in the positive axial direction.

[0080] The use of multiple anode lead tabs 7 for connecting the anode foil 3 allows for the use of a long and wide foil 3. The use of multiple tabs 7 also reduces the metal resistance of the wound element 2, allowing current to be supplied to the wound element 2 at multiple positions, thereby limiting the length that the current must travel inside the wound element 2.

[0081] The conductive lead tabs 7, 8 are configured as flexible metal strips with one side fixed to the anode foil 3 or cathode foil 4 and the other side fixed to an external contact.

[0082] The external contact may be a separate element, or preferably may be integrated into the cover or bottom of the can.

[0083] The anode lead tab 7 electrically and mechanically connects the anode foil 3 to an external contact.

[0084] The metal strip of the anode lead tab 7 includes a conductive metal, and in this embodiment, the metal strip includes aluminum (Al) as the main material.

[0085] Specifically, the anode lead tab 7 comprises a high surface area aluminum foil.

[0086] To provide a high surface area aluminum foil, the normally smooth surface of the aluminum foil is roughened by chemical etching, electrochemical etching, mechanical treatment, plasma treatment, laser treatment, or a combination of the above processes until a surface area of ​​the roughened surface is achieved that is at least 5 times greater than the specific surface area of ​​the smooth surface.

[0087] Preferably, the area is at least 10 times greater than the specific surface area of ​​the smooth surface.

[0088] The specific surface area is the ratio of the absolute surface area to the projected surface area.

[0089] By roughening the surface, 3 μF / cm 2 or more, preferably 5 μF / cm 2 or more, or more preferably 30 μF / cm 2 The specific capacity of aluminum foil is directly proportional to its specific surface area.

[0090] The entire wound element 2, including the anode lead tab 7, is impregnated with liquid electrolyte.

[0091] With modern smooth lead tab surfaces such as those shown in Figure 2, electrochemical corrosion by halogen anions or halogen-containing organic halogen compounds can cause the anode lead tab to disintegrate.

[0092] The amount of halogen contained in the raw materials of aluminum electrolytic capacitors cannot be completely eliminated. Therefore, the surfaces of the electrolyte 6 and the anode lead tab 7 contain at least a small amount of halogen, typically about 0.1 to 0.2 mg / m 2 (halogen / surface of anode lead tab 7), or 0.1 to 0.2 mg / kg (halogen / electrolyte), preferably 0.5 mg / m 2(halogen / surface of anode lead tab 7) or 0.5 mg / kg (halogen / electrolyte) of halogen.

[0093] On the other hand, small amounts of halogens such as Cl, Br, I and F ions can initiate corrosion reactions.

[0094] The most abundant halogen is Cl, which is a natural impurity in nearly all raw materials. The reaction of halogen ions with the aluminum anode lead tab 7 is self-accelerating, causing premature failure of modern capacitors as the capacitor temperature and applied voltage increase.

[0095] The reaction of halogens with metal Al produces soluble Al salts of halogen ions in a relatively fast reaction (R2). Aluminum oxide also reacts with halogen ions in the presence of an acidic electrolyte in a relatively slow reaction (R1). Common electrolytes include, for example, carboxylic acids and / or dicarboxylic acids and / or boric acid. Water, which is always present in the electrolyte, can also function as an acid.

[0096] In the presence of water, the halogen ions dissociate again in reaction R3, initiating a new reaction with aluminum or aluminum oxide (R1, R2). Ultimately, a chain reaction is initiated. A low water content in the electrolyte also triggers the aforementioned reaction. All common electrolytes contain at least a small amount of water. The typical proportion of water in an electrolyte is between 0.5% and 16%, and for electrolytes used in high-voltage capacitors, it is preferably between 3% and 5%.

[0097] In the following formula, X represents any halogen (Cl, Br, I, F). Al2O3+ 6H + + 6X - → 2AlX3+ 3H2O(R1) Al + 3X - → AlX3+ 3e - (R2) 2AlX3+ 6H2O → 2Al(OH)3+ 6H + + 6X - (R3)

[0098] In the reaction, electrons of R2 are accepted by the anode, causing more negatively charged anions to accumulate at the reaction site.

[0099] If the concentration of halogen ions at a certain location on the surface is too high, the metallic aluminum will react completely and so-called clusters will form, which will lead to damage to the aluminum foil and even the anode lead tab.

[0100] In particular, cracks or voids 9 in the oxide layer, which cannot be completely avoided, lead to the formation of such clusters.

[0101] FIG. 2 shows the anode lead tab surface with an oxide layer exhibiting the aforementioned voids and cracks.

[0102] On the other hand, if the concentration of halogen ions on the surface is low, the acid in the electrolyte reacts with the aluminum in a relatively slow reaction, forming an aluminum oxide layer that protects the aluminum material of the anode tab 7 from external chemical agents.

[0103] For example, aluminum can react with the oxidizing dicarboxylic acid or boric acid of the liquid electrolyte: 2Al + 3O 2- → Al2O3+ 6e -

[0104] As shown in Figure 3, the high surface area of ​​the roughened aluminum foil allows the halogen ions to be distributed uniformly on the surface, and clusters with locally high current density do not reach the surface. By increasing the specific surface area by 10 times, the specific surface area can be increased to preferably 0.05 mg / m. 2 The surface concentration of halogen may be reduced to less than 0.5 W. Thus, the chain reaction described above is slowed down due to the locally restricted halogen ions.

[0105] In this case, even at high temperature and high voltage, the electrolyte oxidizes the surface of the anode lead tab 7 faster than the oxide layer, or the aluminum foil itself is damaged by halogen ions due to the extremely low halogen concentration.

[0106] The thickness of the oxide layer is preferably greater than 3 nm.

[0107] Typical operating conditions for the aforementioned capacitors are high voltages of 550V or more and temperatures of about 105°C.

[0108] The life of the aforementioned capacitor before the anode lead tab fails is greater than 3000 hours, and preferably greater than 5000 hours. [Explanation of symbols]

[0109] 1 electrolytic capacitor 2. Wound element 3 Anode foil 4 cathode foil 5 Separator 6 Electrolytes 7 Anode lead tab 8 Cathode lead tab 9. Cracks in the oxide layer

Claims

1. an anode lead tab, configured to externally contact the anode foil within the electrolytic capacitor; providing a roughened surface that protects the anode lead tab from surface dissolution; the specific surface area of ​​the roughened surface is at least 10 times greater than the specific surface area of ​​the smooth surface; the anode lead tab contains aluminum as a primary material; The anode lead tab, wherein the roughened surface is passivated by an aluminum oxide protective layer that forms spontaneously in an atmospheric environment.

2. The specific capacitance of the roughened surface is 3 μF / cm 2 The anode lead tab according to claim 1 .

3. An aluminum electrolytic capacitor having the anode lead tab according to claim 1.

4. 10. An aluminum electrolytic capacitor having at least two anode lead tabs according to claim 1.

5. 1. A method of manufacturing an anode lead tab that provides a roughened surface, comprising: providing an anode lead tab having a smooth surface; 3 μF / cm 2 roughening the smooth surface by one or more of chemical etching, electrochemical etching, mechanical treatment, plasma treatment, or laser treatment until a specific capacitance equal to or greater than 1000 kJ / cm is achieved, wherein the roughened surface is passivated by a protective aluminum oxide layer formed spontaneously in an atmospheric environment; and A method wherein the specific surface area of ​​the roughened surface is at least 10 times greater than the specific surface area of ​​the smooth surface.

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