Electrode, electrolyte, capacitive element, capacitor, and method for producing or modifying or impregnating an electrode

Abstract

Electrodes, electrolytes, capacitive elements, capacitors, and methods of making or modifying or impregnating electrodes.SOLUTION: According to the present application, an electrode is provided having a substrate and a sintered body on a first major surface of the substrate. The substrate includes a first valve metal. The sintered body comprises fused or sintered particles comprising a second valve metal. The first major surface of the substrate is surface modified.SELECTED DRAWING: Figure 2

Description

Detailed Description of the Invention

[0001] FIELD OF THE INVENTION This application relates to electrodes, electrolytes, capacitive elements, capacitors, and methods of forming, modifying, or impregnating electrodes.

[0002] Improvements in capacitors in general, and electrolytic capacitors in particular, can present challenges. In particular, attempts to improve the volumetric efficiency of capacitors can lead to secondary problems.

[0003] For example, the present inventors have found that at least some capacitors with high volumetric efficiency tend to have problems, one of which, in particular, can be a shortened lifetime under the same operating conditions as less volumetrically efficient capacitors.

[0004] Other challenges may arise, particularly when sintered anodes or the like are used in capacitors.

[0005] It is therefore an object of the present application to provide an electrode or capacitor that solves, at least in part, one of the problems mentioned above or described below.

[0006] The electrode, electrolyte, capacitor or capacitive element or method of the independent claims respectively solves at least partly the problems addressed above or below. Advantageous embodiments are provided in the dependent claims.

[0007] Below, certain features are disclosed which, when taken alone, can provide benefits such as those mentioned above or other benefits that will be described below, however, particularly when combined, synergistic and additional benefits can be realized.

[0008] According to a first embodiment, which may be applied to, but not necessarily all other embodiments below, a sintered electrode is described.

[0009] In the most general sense, a sintered electrode is an electrode having a sintered body. The sintered electrode can be used in a capacitor, preferably an electrolytic capacitor. The sintered electrode preferably includes a valve element. This can mean that it can include one or more valve elements.

[0010] One or more different types of particles, including or consisting of valve metal, are sintered or fused together to form a sintered body. "Fused" herein means that the particles in the sintered body do not break apart but are incorporated into a solid, preferably partially fused together with other particles, into a porous structure of fused particles. Such a sintered body of fused particles can generally be achieved by any means. In particular, it may be achieved by sintering valve metal particles, i.e., by a heating or annealing step that causes the particles to coalesce or fuse. This means that the term "sintered body" is not limited to a body of particles that are actually sintered. Any other technique that leads to a similar coalescence of particles can form a sintered body, even if, for example, no heat treatment is applied. However, sintering is the most preferred technique.

[0011] The inventors of the present invention have found that sintered electrodes can help increase the volumetric efficiency of a capacitor, particularly when used as an anode. In particular, improved volumetric efficiency can be found when compared to etched electrodes. Electrodes, particularly those used as anodes, are preferably passivated with an oxide layer.

[0012] Here and below, the term "valve metal" is understood in its general technical sense and is not otherwise limited. For example, the valve metal includes at least aluminum, titanium, tantalum, niobium, tungsten, chromium, zirconium, hafnium, zinc, vanadium, bismuth, or antimony. Among these, aluminum, tantalum, and vanadium are particularly preferred. The most preferred valve metal for use in the electrodes of the embodiments disclosed herein is aluminum.

[0013] According to an embodiment, the electrode is a sintered bulk anode, which means that in this case the majority of the volume of the anode may consist of a sintered body or sintered material, in which case the sintered material block may be contacted with a lead terminal or the like.

[0014] According to other embodiments of the present specification and according to even more preferred embodiments, the sintered anode may have a substrate. The substrate can in principle comprise any conductive material, such as a metal or alloy, or can consist solely of these conductive materials. Preferably, the substrate also comprises or consists of a valve metal, which may be referred to herein as the first valve metal. The valve metal of the particles of the sintered body may in this case be referred to as the second valve metal. In both cases, the first valve metal and the second valve metal may be individually selected from the valve metals listed above. Most preferably, they are the same. Even more preferably, they are both aluminum.

[0015] The sintered body can be arranged on the main surface of the substrate. For example, the substrate can be a small plate or foil, and the sintered body can be a sintered layer arranged on the main surface of the foil. Even more preferably, the two opposing main surfaces of the substrate foil can be covered with a sintered layer. Such a configuration can enable an improved specific capacity that is higher than can be achieved by, for example, an etching anode.

[0016] The inventors of the present invention have discovered that electrodes having a substrate in the above-described sintered body may, in some cases, lack adhesion between the sintered body and the surface. In some cases, the sintered body may delaminate from the substrate. This can occur, for example, during processing of the electrode foil, such as slitting, winding, and cold welding processes, as well as during operation of the capacitor. In addition to affecting the quality of the electrode and the capacitor constructed therewith, the delaminated portion may also generate gas during storage or operation of the capacitor. Delamination can expose metal that is oxidized by the electrolyte, which, for example, generates gas. Such gas can lead to a buildup of pressure within the capacitor, which can destroy the capacitor.

[0017] To at least partially overcome this problem, the inventors have surprisingly found that by surface-modifying the first main surface of the substrate, the sintered body arranged on said main surface can have improved adhesion, and delamination can thus be better prevented.

[0018] According to embodiments, the surface modification can increase the surface area or roughness of the first major surface of the substrate. A point of comparison can be the unmodified substrate surface. The inventors believe that the increased surface area can help increase adhesion.

[0019] According to an embodiment, the surface modification may include protruding portions. Protruding portions may be any portions produced by the surface modification that protrude above the average level of the modified surface. According to a preferred variant of this embodiment, some protruding portions may be tip-molded and / or rim-molded. Generally, protruding portions may have a smaller thickness along at least one direction at a point facing farthest away from the substrate than at a point facing further towards the substrate.

[0020] According to embodiments, the surface modification can include indentations into the substrate. For example, the indentations can have a concave shape. In particular, it is believed that it is preferable for these indentations into the substrate to have a crater-like shape.

[0021] In a modification of the above-described embodiment, and in an embodiment where the surface is modified to include an indentation, the protruding portion may be a rim or tip portion of a crater-like indentation.

[0022] The inventors have found that adhesion can be improved by having some or all of the above-mentioned surface morphology characteristics. For example, indentations may help accommodate particles. Protruding portions may provide portions of the modified substrate surface that heat up to the sintering temperature more quickly during the sintering procedure, allowing for the sintered body to simply be sintered onto the major surface.

[0023] Thus, in general, the embodiments of the present description are also configured with surface modifications to improve adhesion during sintering.

[0024] The formation of said surface modifications is not limited in the most general sense to any type of specific structure, nor to any type of method for producing said structure, in particular the technique may include, for example, a lithography step.

[0025] According to a preferred embodiment, the surface modification is or is achieved by chemical or electrochemical surface etching. In particular, in valve metal-containing surfaces, most preferably aluminum-containing surfaces, indentations can be easily etched therein by chemical or electrochemical means. The rim of the indentation can form a protruding portion. In this way, a simple process for achieving surface modification can be realized.

[0026] Surface modification in general, and etching in particular, can also be advantageous as it can at least partially remove any native oxides formed or impurities on the substrate surface.

[0027] According to the embodiment, the surface roughness R of the surface-modified main surface aThe surface roughness R may be of the same order of magnitude as the grains of the sintered body, or may be smaller. The term "of the same order of magnitude" can be understood in the usual technical sense of the word. For example, this means the average size of the structures on the surface, and the surface roughness R a The surface roughness may be 0.1 to 10 times the average particle size used. Alternatively or additionally, the surface roughness may be 0.01 to 50 μm in size. More preferably, it may be 0.1 to 50 μm, 0.5 to 10 μm, or even 0.7 to 7 μm, or 0.5 to 5 μm.

[0028] The inventors of the present invention have found that adhesion can be favorable when the size of the structures on the surface is similar to that of the particles used in the sintered body.

[0029] According to an embodiment, the grains of the sintered body have an average size between 0.5 μm and 10 μm, for example between 1 μm and 5 μm.

[0030] The inventors have found that this grain size for the particles of the sintered body helps to increase the volumetric efficiency of the electrode. The inventors have further found that particles of this size can be adhered well by the above-defined means. In particular, the structure produced by etching and / or the above-mentioned surface roughness regime provides good adhesion for particles of this size.

[0031] According to a further embodiment, the content of the valve metal in the substrate can be 98% by weight or more, for example, 99% by weight or more, or even more preferably 99.7% by weight or more, or even more preferably 99.9% by weight or more. These values ​​are particularly relevant for the valve metal aluminum. High-purity valve metal substrates must often be used to produce sintered electrodes. These are more expensive to manufacture than the above-mentioned substrates with lower purity. Furthermore, the inventors have found that lower purity of the substrate can help surface-modify the substrate.

[0032] According to embodiments, for the reasons described above, the purity of the valve metal in the substrate can be less than 99.99 wt.%, and more preferably less than 99.9 wt.%. Thus, for example, a range of 98 wt.% to 99.90 or 99.99 wt.% can be used. Alternatively, the above values ​​can be substituted for "98%" in this range. In particular, with respect to the range of 99.7 wt.% to 99.99 wt.% or 99.7 wt.% to 99.90 wt.%, the inventors have found that the impurity level is good for surface modification but not too high, and other drawbacks of the impurities are reduced.

[0033] The following embodiment is also preferably used for electrodes having the above-mentioned sintered body. However, this approach can also be applied to any other type of electrode that can be used in an electrolytic capacitor. Electrodes may have defects or cracks for several reasons. At these defects or cracks, the oxide layer that is preferably formed on the surface of the electrode may be partially absent.

[0034] The inventors have found that the sintered body described above is particularly prone to the formation of cracks described above. For example, cracks may form as a result of the manufacturing process of the electrode. For example, in the case of a foil electrode having a foil-like substrate and a sintered body, cracks or partial delamination of the sintered body may occur during process steps such as slitting, winding, and cold welding processes, as well as during subsequent operation of the capacitor.

[0035] According to embodiments of the present invention, such cracks, or any sites at least partially lacking an oxide layer, can be at least partially passivated using a passivating compound.

[0036] If not quickly passivated, gases can form at these sites during operation or even passive storage due to chemical reactions with the exposed metal. Thus, unwanted excess gas can form within the capacitor and destroy the capacitor. An exhaust system may be used to accommodate such gas formation. Passivating the sites thus helps reduce gas generation and may also help avoid complex gas compensation measures.

[0037] Until now, the high energy density or capacity density of sintered anode foils, combined with numerous surface cracks, has led to high energy consumption or leakage current until the damaged electrode has sufficient passivation oxide. Prior art electrodes typically require multiple repairs during the capacitor's lifetime, and the resulting high hydrogen gas evolution limits the applicability of this technology. These drawbacks can be reduced by using passivation compounds.

[0038] As described in more detail below, the materials can be applied separately prior to assembly of the capacitor, either onto the anode or directly onto a capacitive element such as a wire wound element, or they can be applied as components of the electrolyte itself.

[0039] The inventors have found that the passivating compound can reduce gassing before and during oxide formation that may occur from the liquid electrolyte, meaning that in addition to the passivating effect of the compound itself, the combination of the passivating compound and the oxide that forms can further facilitate site closure.

[0040] Passivation compounds are generally not limited and can be applied in the form of molecular or particle-containing compounds or complexes.

[0041] According to embodiments, a phosphorus-containing compound or a silicon-containing compound may be used as the partial passivation compound described above.

[0042] For example, according to embodiments, the silicon-containing compound can be provided in the form of particles, such as particles that can contain silicon oxide.

[0043] According to an embodiment, the application of a passivation compound can also reduce the demand for a high purity level for the valve metal of the electrode. In the case of a sintered electrode having a substrate and a sintered body, this can be applied to the substrate and / or the sintered body. For example, the passivation compound may be helpful when using a valve metal purity of 99.7% or 99.8% by weight or higher, for example, 99.7 to 99.99% by weight or 99.7 to 99.0% by weight. The inventors have found that the passivation component can help reduce leakage current in combination with reduced purity. This applies to both the substrate and the sintered body. In both cases, the effect is particularly pronounced for Al.

[0044] According to embodiments, it may be preferable to combine surface modification and passivation, both of which can help reduce the free metal surface in a complementary manner. Both measures may help to use less pure metal.

[0045] Furthermore, the inventors have found that the thickness of the separator can be reduced through better passivation by using a passivation compound in the capacitor device. This can increase volumetric efficiency. For example, this may help reduce the separator thickness to 44 μm or less, or 40 μm or less, or even 35 μm or less. These values ​​may be the total thickness of the separator between the anode and cathode foils. Here and throughout this specification, the term "separator" may refer to a functional unit that separates the cathode and anode. It is not limited to a single-layer separator, but may include separator structures having two or more layers.

[0046] According to a further embodiment, an electrode is described that has an impregnation on at least a part of its surface. Again, the electrode is preferably an electrode with an impregnated sintered portion, but is not limited to such sintered electrodes. The impregnation is configured to increase the wettability of the electrode or the impregnated portion by the electrolyte. The inventors have found that by increasing the surface area of ​​the electrode, for example, in particular by having a sintered body, the wettability of the electrode by the electrolyte becomes increasingly important.

[0047] The inventors have found that the high degree of compaction and density of sintered electrodes and the oxides grown on them can make wetting by the electrolyte difficult, especially for electrolytes with higher viscosities, which can be improved by impregnation compounds.

[0048] According to embodiments, silanes can act as wettability-improving impregnating agents. The same is true for polyethylene oxides, sulfonates, or anionic surfactants. Silanes, polyethylene oxides, sulfonates, or anionic surfactants can be used individually, or mixtures of one or two of them can also be used.

[0049] The above-mentioned approaches to increasing wettability can preferably also be applied to the above-mentioned surface modifications and, in a complementary manner, to the reduction of non-passivated sites.

[0050] Additionally, an electrolyte for an electrolytic capacitor is described as a further embodiment.

[0051] According to a first embodiment, an electrolyte is described that includes a compound configured to adsorb to crack sites of an electrode or to sites of an electrode that are at least partially devoid of an oxide layer, the compound configured to at least partially passivate said sites. Electrolytes that may be used in electrolytic capacitors can include the at least partially passivating compounds described above.

[0052] The advantages mentioned above also apply here.

[0053] According to embodiments, the passivation compound can be a phosphorus- or silicon-containing compound, either molecular or particulate, as described above. In the latter case, the electrolyte can be an emulsion containing said particles. For example, particles containing silicon oxide can be used in a concentration ranging from 0.1 to 5% by weight, e.g., 0.5 to 1.5% by weight.

[0054] For example, an electrolyte may be combined with the above-described electrodes, preferably sintered electrodes, in a capacitor. Thus, the above-described partially passivated electrodes can be formed in situ by the electrolyte. In many cases, a portion of the passivating compound can be found in the electrolyte even after adsorption onto the electrode.

[0055] According to a further embodiment, an electrolyte for an electrolytic capacitor is described having an impregnation compound configured to impregnate a portion of a surface of an electrode. The impregnation compound is configured to increase the wettability of the surface of the electrode by the electrolyte. The compound is further configured to adsorb to the surface of the electrode. For example, the compound may be the above-mentioned silane, polyethylene oxide, sulfonate, and / or anionic surfactant added to the electrolyte.

[0056] According to embodiments, the concentration of the impregnation compound in the electrolyte can be 10 to 200 ppm by weight, for example 15 to 50 ppm. In general, but particularly for the example impregnation compounds listed, the inventors have found that this concentration range results in significantly improved wettability by the electrolyte.

[0057] For example, the electrolyte may be combined with the electrolyte, preferably a sintered electrode, in a capacitor. Thus, the impregnated electrode may be formed in situ with the electrolyte. In many cases, the impregnating compound may be found in the electrolyte even after adsorption onto the electrode.

[0058] The impregnation compound and the passivation compound may be added together to the electrolyte.

[0059] According to a further embodiment, which can be independent of the other embodiments described above but can also be advantageously combined with them, an electrolyte for an electrolytic capacitor is described, which has a conductivity of 660 μS / cm or less at a temperature of 30° C. before wetting the separator or wetting the winding elements. The inventors of the present invention have found that a conductivity of 660 μS / cm or less can be advantageous for sintered electrodes and can help reduce the thickness of the separator immersed in the electrolyte.

[0060] Having a lower conductivity can reduce the generation of localized heat during self-healing or reduce the need for passivation processes of damaged sintered bodies as described above. Until the present invention, highly conductive electrolytes were often used to allow surface repair processes to generate high density localized heat, resulting in very high leakage currents.

[0061] According to a variation of the above embodiment, the electrolyte can have a water content of 1% to 10%. The inventors of the present invention have found that such a high water content in the electrolyte can help reduce the thickness of the separator paper.

[0062] According to further embodiments, a capacitive element is described. The capacitive element may be configured to store charge during operation of the capacitor. For example, the capacitive element can be configured to charge and discharge during operation of the capacitor. For example, the capacitive element can include a cathode and an anode. The cathode and anode can be in electrical contact by a conductive element such as a wire or lead. The cathode and anode are generally not limited. Preferably, the anode can have the properties of the electrodes described above.

[0063] According to an embodiment that may be preferred over other embodiments, the capacitive element may be a winding element around which the anode and cathode are wound, for example the winding element may be a cylindrical winding element or a flat winding element.

[0064] According to an embodiment that is believed to be preferred for other embodiments, the winding elements can be configured for an electrolytic capacitor. In this case, an electrolyte is disposed between the anode and the cathode. For example, a separator wetted or immersed with the electrolyte may be disposed between the anode and the cathode. The separator is not limited other than that it should be configured to be immersed or wetted by the electrolyte and should not be electrically conductive. The separator may include or consist solely of a cellulosic material such as paper. In an electrolytic capacitor, it is believed to be preferred that the anode have an oxide on its surface that provides at least partial chemical and electrical isolation between the anode and the electrolyte.

[0065] The electrolyte is generally not limited, and may further have the electrolyte characteristics described above that lead to desirable benefits.

[0066] According to an embodiment, a capacitive element can be described in which the separator is immersed in an electrolyte having a maximum conductivity of 660 μS / cm and preferably also in a water content of 1 to 10%. In this case, the thickness of the separator can be 44 μm or less. For example, the thickness of the separator can be 40 μm or less, and even 35 μm or less.

[0067] According to a further embodiment, a capacitor is provided having a capacitive element. The capacitive element may be one of the capacitive elements described above or may have a combination of features thereof. Alternatively, or in addition, the capacitor may have any of the electrodes described above as an anode. Alternatively, or in addition, the capacitor may have any electrolyte, but preferably has one of the electrolytes described above.

[0068] According to further embodiments, a process for manufacturing an electrode or a process for treating an electrode is described below. Where applicable, the process can have the above-mentioned features described with respect to the electrode or electrolyte.

[0069] According to an embodiment, a process for manufacturing an electrode is described. First, a substrate is prepared. The substrate used herein may include or consist exclusively of a first valve metal. For example, it may include aluminum or consist primarily of aluminum. For example, the substrate may have the purity level described above. In a further step, the main surface of the substrate is modified to receive a surface-modified main surface of the substrate. For example, as described above, the surface modification may be the formation of protrusions and / or indentations to increase surface roughness, preferably adhesion to the sintered body. In the next step of the process, a sintered body is formed on the surface-modified main surface. The sintered body may include or consist exclusively of fused particles including or consisting exclusively of a second valve metal. The partial process for forming the sintered body is not limited and can be any suitable process. For example, forming the sintered body may include sintering particles at a temperature of 400 to 660°C. The particles may, for example, include aluminum as a primary component. For example, forming the sintered body may include depositing a slurry containing the particles. The slurry may then be sintered. The particles generally comprise a second valve metal, preferably aluminum.

[0070] As mentioned above, surface modification can be achieved by any suitable means, such as lithography or any type of etching. Most preferably, chemical or electrochemical etching is used.

[0071] According to a further embodiment, a process is described in which at least a portion of a sintered body is modified by adsorbing a compound at crack sites or at least at sites at least partially lacking an oxide layer. The compound is configured to at least partially passivate said sites. The properties described above regarding such compounds may apply here. This process may be performed on the as-formed electrode, or by having an at least partially passivating compound in the electrolyte, or a combination of both.

[0072] According to a further embodiment, a process for impregnating at least a portion of an electrode, preferably a sintered body, is described. This impregnation can be carried out by applying an impregnation compound, which can be an impregnation compound as described above. The impregnation compound is configured to increase the wettability of the surface of the electrode by the electrolyte. This process can also be carried out before assembling the electrode into a capacitor, or by having the impregnation compound in the electrolyte, or a combination of both.

[0073] Further advantageous and further embodiments of the electrode or capacitor and the method for producing such an electrode or capacitor can be seen from the following exemplary embodiments described in connection with the figures. However, it should be noted that the present invention is not limited to said exemplary embodiments. Furthermore, said exemplary embodiments are at least partially illustrated in figures showing schematic diagrams. These schematic diagrams are not to scale, and absolute and relative dimensions may be shown distorted. Furthermore, individual elements may be shown greatly exaggerated for better visibility or understanding. Therefore, absolute or relative dimensions cannot be inferred from the schematic diagrams unless otherwise indicated. Elements that are identical, similar, or have the same effect are designated by the same reference signs in the figures. [Brief explanation of the drawings]

[0074] [Figure 1] FIG. 1 shows a schematic sketch of the process of surface modification. [Figure 2] 1 shows a schematic cross section of a first embodiment of an electrode. [Figure 3] FIG. 10 shows a cracked embodiment of an electrode. [Figure 4] 1A-1C show intermediate stages of at least partially passivating the electrodes. [Figure 5] FIG. 1 illustrates an at least partially passivated embodiment of an electrode. [Figure 6] FIG. 1 shows a schematic diagram of the wetting behavior of a non-impregnated electrode. [Figure 7] FIG. 1 shows the wetting behavior of an impregnated electrode. [Figure 8] 1 illustrates an exemplary embodiment of a capacitor.

[0075] FIG. 1 shows a schematic cross-section of a process for forming a surface-modified substrate. On the left-hand side of the figure, substrate 1 is shown having a first major surface 2 and a second major surface 3. Substrate 1 consists solely of a material containing 99.7% or more aluminum by weight. It is then chemically or electrochemically etched. In particular, electrochemical etching can be performed in a process similar to the formation of a cathode in forming an electrolytic capacitor. A modified first major surface 2' is then formed from first major surface 2. A modified second major surface 3' is then formed from second major surface 3. The resulting structures include tip- or rim-shaped protrusions, as well as recessed or bowl-shaped indentations in the substrate.

[0076] Chemical etching can be carried out in HCl or NaOH solution. The concentration can be between 0.5 mol / l and 4 mol / l, for example, preferably 1 mol / l. Etching is carried out at a temperature of 60°C, but can also be carried out at other temperatures, for example. Electrochemical etching is carried out under essentially the same conditions and at 100 mA / cm. 2 ~3A / cm 2 The conditions can be selected or configured to produce the structures described.

[0077] In a further step, the result of which is shown in FIG. 2, a first sintered body 4 and a second sintered body 5 can be formed on the first and second modified main surfaces 2' and 3'. The sintered bodies 4 and 5 are formed from aluminum particles provided in a slurry. The slurry is deposited on the modified substrate surfaces 2' and 3'. The slurry can then be debindered and sintered. Sintering is carried out at a temperature between 400 and 660°C. The particles of the sintered bodies 4 and 5 become fused together by sintering. The particles are aluminum-based particles with an aluminum content of 99% by weight or higher. It is not explicitly stated here that aluminum sintered bodies can be passivated by oxidation, whereby an insulating surface oxide is formed.

[0078] By having the above-mentioned surface modification, the adhesion of the sintered body to the surface can be improved. The inventors believe that this is due to the increased surface roughness and possibly also to the removal of native oxides and potential impurities on the substrate. Furthermore, the inventors have found that the above-mentioned relatively low purity of the substrate simplifies the formation of the surface modification.

[0079] The process of passivating crack sites is illustrated in Figures 3-5. Figure 3 shows a substrate 1 having a surface-modified major surface 2' as described above with reference to Figures 1 and 2. A sintered body 4 is formed on the substrate 1. The sintered body is composed of fused particles 6. A surface oxide 7 is clearly visible here. The sintered body can be damaged during the fabrication steps of forming the capacitor, such as slitting, winding, and cold welding. This can result in the formation of crack sites 8. As shown in Figure 4, a component configured to at least partially passivate these crack sites 8 can be adsorbed to these crack sites 8. This can be done in the capacitor electrolyte, or additionally or alternatively, before adding the electrolyte. Here, a passivation compound 9 is formed from silicon oxide particles. These can be present in an emulsion-like electrolyte or can be added in a separate emulsion before potting the capacitor. Such silicon oxide or phosphorus-containing compounds or particles adhere to the crack sites and form modified crack sites 8', as shown in Figure 4. This already partially provides passivation to these crack sites. This may reduce gas formation from electrolyte reactions within the assembled capacitor.

[0080] As shown in FIG. 5, by applying a suitable solution, or in particular an electrolyte containing some water, a partial oxide 10, indicated by the dashed line, can be formed in addition to the silicon particles 9. This oxide can at least partially and further passivate the group sites. The inventors have found that by using an at least partially passivating compound such as silicon oxide, passivation by the newly formed oxide in the electrolyte or by other individual techniques can better passivate the crack sites. Here, the crack sites have the reference numeral 8″, indicating increased passivation.

[0081] In Figure 6, the sintered electrode is shown immersed in electrolyte, where the electrolyte 11 has problems completely wetting the entire sintered body.

[0082] To overcome this, the inventors have found that an impregnation compound 12 can be adsorbed onto the particles 6 of the sintered body, as shown in Figure 7. This can be done before potting the capacitor, or by adding such a compound to the electrolyte. In the case of the electrolyte, the concentration of the impregnation compound can be 10-200 ppm by weight. As shown, wetting by the electrolyte is improved, thereby allowing a larger portion of the capacitor to be used for capacitive interaction.

[0083] In FIG. 8, a capacitor 13 is shown in schematic cross section. The capacitor 13 has a case 14 sealed by a cover 15. A winding element 16 is assembled within the housing formed by the case 14 and cover 15. Although not explicitly shown, the winding element includes a cathode, which may be any of the anodes described above. Two lead contacts 17 are provided to connect the anode and the cathode. The anode and cathode in the winding element are further separated by separator paper. The separator paper is immersed in an electrolyte. Optionally, the electrolyte can contain the aforementioned substances for crack passivation and to increase wettability. Furthermore, the electrolyte used herein preferably has a conductivity of 660 μS / cm or less and a water content of 1 to 10%. Therefore, the thickness of the separator paper can be reduced to 40 μm or even less. [Explanation of symbols]

[0084] 1 Base material 2 First main surface 2' modified first major surface 3 Second main surface 3' modified second major face 4. First sintered body 5 Second sintered body 6 particles 7. Oxides 8 Crack location 9 Passive compounds 10 partial oxide 11 Electrolytes 12 Impregnation compound 13 Capacitor 14 cases 15 Cover 16 winding elements 17 Lead Contact

Claims

1. 1. An electrode having a substrate and a sintered body on a first major surface of the substrate, the substrate comprises or consists solely of a first valve metal; the sintered body comprises or consists solely of fused or sintered particles, the particles comprising or consisting solely of a second valve metal; An electrode, wherein the first principal surface is surface-modified.

2. 10. The electrode of claim 1, wherein the surface modification is an increase in surface area and / or surface roughness compared to an unmodified substrate surface.

3. 3. The electrode of claim 1 or 2, wherein the surface modification is configured to increase adhesion of the sintered body or of particles of the sintered body to a surface compared to an unmodified substrate surface.

4. The electrode according to any one of claims 1 to 3, wherein the surface modification comprises protruding portions.

5. 5. The electrode according to claim 1, wherein the surface modification is chemical or electrochemical surface etching.

6. The electrode of any one of claims 1 to 5, wherein the surface modification comprises indentations in the substrate.

7. The surface roughness R formed by the surface modification ａ 7. An electrode according to claim 1, wherein is on the same order of magnitude as or smaller than the average grain size of the particles of the sintered body.

8. 8. An electrode according to any one of the preceding claims, wherein the grains of the sintered body have an average size between 0.5 μm and 20 μm.

9. 9. An electrode according to any one of the preceding claims, wherein the content of said valve metal in said substrate is 98% by weight or more, preferably 99.7% by weight or more.

10. 10. The electrode according to claim 1, wherein the content of the valve metal in the substrate is 99.99% by weight or less.

11. 1. An electrode comprising a sintered body, the sintered body comprises or consists of fused or sintered particles, the particles comprising or consisting of a valve metal; an electrode, wherein a compound is adsorbed at crack sites of the sintered body or at sites of the sintered body that are at least partially devoid of an oxide layer, the compound being configured to at least partially passivate the sites.

12. 1. An electrode comprising a sintered body, the sintered body comprises or consists of fused or sintered particles, the particles comprising or consisting of a valve metal; An electrode, wherein a phosphorus-containing compound or a silicon-containing compound is adsorbed at crack sites of the sintered body or at sites of the sintered body that are at least partially devoid of an oxide layer.

13. 13. The electrode of claim 11 or 12, wherein the compounds adsorbed at crack sites comprise molecular and / or particulate compounds and / or complexes.

14. Electrode having the features of at least one of claims 11 to 13 in combination with at least one of claims 1 to 10.

15. 1. An electrode having an impregnation on at least a portion of its surface, said impregnation configured to increase wettability by an electrolyte.

16. 16. The electrode of claim 15, wherein the impregnation comprises polyethylene oxide, a sulfonate, and / or an anionic surfactant.

17. Electrode having the features of claim 15 or 16 in combination with at least one of claims 1 to 10.

18. Electrode having the features of claim 15 or 16 in combination with at least one of claims 11 to 14.

19. 1. An electrolyte for an electrolytic capacitor, comprising a compound configured to adsorb to cracked regions of an electrode or regions of an electrode that are at least partially devoid of an oxide layer, the compound configured to at least partially passivate the regions.

20. An electrolyte for an electrolytic capacitor comprising a phosphorus-containing compound or a silicon-containing compound.

21. 1. An electrolyte for an electrolytic capacitor, the electrolyte comprising an impregnation compound configured to impregnate a portion of a surface of an electrode, and configured to increase wettability of the surface of the electrode by the electrolyte when adsorbed on the surface of the electrode.

22. 22. The electrolyte of claim 21, wherein the concentration of the impregnation compound is from 10 to 200 ppm by weight.

23. 1. An electrolyte for an electrolytic capacitor, wherein the electrolyte has a conductivity of 660 μS / cm or less at a temperature of 30° C. before wetting the separator or wound elements.

24. 24. The electrolyte for an electrolytic capacitor of claim 23, having a water content of 1% to 10%.

25. A capacitive element comprising an electrode according to at least one of claims 1 to 18 as an anode.

26. A capacitive element comprising an anode, a cathode, and an electrolyte according to any one of claims 19 to 24.

27. 27. The capacitive element of claim 26, wherein a separator immersed in the electrolyte is disposed between the cathode and the anode, the separator having a total thickness of 44 μm or less.

28. A capacitive element according to any one of claims 25 to 27, comprising an electrode according to at least one of claims 1 to 18 as an anode.

29. A capacitor comprising an electrode according to at least one of claims 1 to 18 and / or an electrolyte according to at least one of claims 20 to 24, or a capacitive element according to at least one of claims 25 to 28, arranged in a housing.

30. providing a substrate comprising or consisting of a first valve metal; surface-modifying a major surface of the substrate to obtain a surface-modified major surface of the substrate; forming a sintered body on the surface-modified main surface; wherein the sintered body comprises or consists of fused or sintered particles, and the particles comprise or consist of a second valve metal. A method for manufacturing an electrode.

31. 31. A method for producing an electrode according to claim 30, wherein the major surface is chemically or electrochemically etched to form the surface modification.

32. 32. The method for manufacturing an electrode according to claim 30 or 31, wherein the step of forming the sintered body comprises depositing a slurry containing particles comprising a second valve metal on the surface-modified major surface.

33. A method of manufacturing an electrode according to any one of claims 30 to 32, wherein the step of forming the sintered body comprises sintering at a temperature of 400 to 660°C.

34. 1. A method for modifying at least a portion of a sintered body of an electrode by adsorbing a compound at a crack site or at a site at least partially lacking an oxide layer, said compound being configured to at least partially passivate said site.

35. A method of modifying at least a portion of a sintered body of an electrode by adsorbing a phosphorus-containing or silicon-containing compound at crack sites or at sites at least partially lacking an oxide layer.

36. A method of impregnating at least a portion of an electrode by depositing an impregnation compound configured to increase the wettability of the surface of the electrode by an electrolyte.

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