CAPACITOR WITH CONDUCTIVE ADHESION LAYER

Abstract

The present invention relates to a capacitor having a metal current collector, a conductive adhesion layer applied on the metal current collector, and an electrode active layer applied on the conductive adhesion layer, wherein the adhesion layer comprises a conductive non-carbide metal compound, particularly a metal oxide or metal nitride. The present invention further relates to a method of manufacture thereof as well a medical device comprising such capacitor.

Claims

1. A capacitor, comprising: a metal current collector, a conductive adhesion layer applied on said metal current collector, and an electrode active layer applied on said conductive adhesion layer, wherein said adhesion layer comprises a conductive non-carbide metal compound, including a metal oxide or metal nitride.

2. The capacitor according to claim 1, wherein said non-carbide metal compound comprises a transition metal, selected from ruthenium, niobium, iridium, manganese, zinc, titanium, zirconium, hafnium, vanadium, tantalum, molybdenum, or tungsten.

3. The capacitor according to claim 1, further comprising an anode essentially consisting of or comprising a valve metal, including tantalum, aluminium or niobium.

4. The capacitor according to claim 1, further comprising an aqueous electrolyte.

5. The capacitor according to claim 1, wherein said conductive adhesion layer comprises a metal oxide, including ruthenium oxide, niobium oxide, iridium oxide, manganese oxide, zinc oxide, or a mixture thereof, and/or a metal nitride, including titanium nitride, zirconium nitride, hafnium nitride, vanadium nitride, niobium nitride, tantalum nitride, molybdenum nitride, tungsten nitride, or a mixture thereof.

6. The capacitor according to claim 1, wherein said conductive adhesion layer has a thickness in the range of 1 nm to 5 μm.

7. The capacitor according to claim 1, wherein said electrode active layer comprises a conductive material selected from carbon, including activated carbon, graphite, graphene, carbon nanotubes, and/or a conductive polymer.

8. The capacitor according to claim 1, wherein said electrode active layer comprises a binder.

9. The capacitor according to claim 8, wherein the binder is selected from polyvinylidene fluoride (PVDF) polytetrafluoroethylene (PTFE), carbomethyl cellulose (CMC) or a rubber, particularly acryl rubber, nitrile butadiene rubber (NBR), styrene butadiene rubber (SBR) or butyl rubber.

10. The capacitor according to claim 1, wherein said metal current collector comprises or essentially consists of titanium or a titanium alloy.

11. The capacitor according to claim 1, further comprising a metal housing, wherein at least a part of said metal housing forms said metal current collector.

12. Method for manufacturing a capacitor according to claim 1, comprising the steps of: applying a conductive adhesion layer on a metal current collector, and applying an electrode active layer on said conductive adhesion layer, wherein said conductive adhesion layer comprises a non-carbide conductive metal compound, including a metal oxide or metal nitride.

13. The method according to claim 12, wherein said conductive adhesion layer is applied on said metal current collector in form of a solution or suspension, wherein said solution or said suspension comprises said non-carbide metal compound and an organic solvent, wherein after application of said conductive adhesion layer said metal current collector is tempered at a temperature below 700° C.

14. The method according to claim 12, wherein said electrode active layer is applied in form of a composition, including paste, comprising a conductive material, including carbon and activated carbon, graphite, graphene, carbon nanotubes, and/or a conductive polymer, and optionally a binder, wherein after applying said electrode layer said metal current collector is tempered at a temperature below 400° C.

15. An implantable medical device, comprising a capacitor according to claim 1.

16. An implantable medical device, comprising a capacitor manufactured by a method according to claim 12.

17. The capacitor according claim 1, wherein said conductive adhesion layer has a thickness in the range of 40 nm to 0.4 μm.

18. The method according to claim 12, wherein said conductive adhesion layer is applied on said metal current collector in form of a solution or suspension, wherein said solution or said suspension comprises said non-carbide metal compound and an organic solvent, wherein after application of said conductive adhesion layer said metal current collector is tempered at a temperature in the range of 360° C. to 550° C.

19. The method according to claim 12, wherein said electrode active layer is applied in form of a composition, including a paste, comprising a conductive material, including carbon and activated carbon, graphite, graphene, carbon nanotubes, and/or a conductive polymer, and optionally a binder, wherein after applying said electrode layer said metal current collector is tempered at a temperature in the range of 80° C. to 240° C.

20. The capacitor according to claim 1, where the capacitor comprises an electrolytic capacitor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Further advantages, features and embodiments of the present invention will be explained hereinafter with reference to the drawings, in which:

[0049] FIG. 1 shows a schematic drawing of the current collector of the capacitor of the present invention;

[0050] FIGS. 2 and 3 show scanning electron microscopic images of nano-structured ruthenium oxide coated surfaces;

[0051] FIG. 4 shows a scanning electron microscopic image of a nano-structured iridium oxide coated surface; and

[0052] FIG. 5 shows cyclic voltammograms of titanium substrates with nano-porous ruthenium oxide, nano-porous iridium oxide coatings and without a coating.

DETAILED DESCRIPTION

Examples

[0053] In a preferred embodiment of the present invention, a conductive metal oxide is applied between a current collector (housing) of a cathode (e.g., of a capacitor) and an additional electrode active coating or layer. This interlayer increases the adhesion of the electrode active coating or layer to the metal current collector and protects the metal current collector from passivation. Particularly, the conductive metal oxide applied as interlayer acts as an adhesion promotor for the electrode active layer, particularly due to its nano-structured surface, and prevents a passivation of the current collector because of its mechanical and chemical stability.

[0054] Accordingly, the present invention provides a mechanically, electrically and chemically stable active layer or coating for a cathode with a high capacitance, which protects a substrate acting as current collector (e.g., titanium housing) from passivation and enables a reliable, long-term stable attachment of an electrode active layer or coating to the substrate.

[0055] Advantageously, such active layer or coating can be manufactured without elevated temperatures (e.g., above 700° C.), which are disadvantageous in terms of costs and impairments of components (warpage of the substrate, housing, cover, etc.; grain growth; large grains can impair the mechanical stability and tightness of components to welded, e.g., housing and cover).

[0056] FIG. 1 illustrates the basic structure of an embodiment of capacitor of the present invention. The capacitor comprises a titanium housing 1, which acts as a current collector. On an inner surface of the housing 1, a metal oxide layer 2 is applied, e.g., ruthenium or iridium oxide, on with a further electrode active layer 3, e.g., activated carbon with a suitable binder, is coated. The capacitor further comprises an anode essentially consisting of or comprising an oxide forming metal 5. Such metal may be a valve metal such as tantalum, aluminium or niobium. The capacitor further comprises a separator 4 to avoid direct electrical contact of the anode 5 with the electrode active layer. Furthermore, an electrolyte fills the space between the anode and the coated titanium housing and establishes thereby an electric contact. Particularly, the afore-mentioned separator is soaked with the electrolyte.

[0057] For manufacturing thereof, a titanium housing 1 was coated with a conductive metal oxide 2, e.g., ruthenium or iridium oxide, and subsequently an electrode active layer 3 comprising activated carbon with a suitable binder (PVDF) was applied. The thereby manufactured graphite electrode is mechanically and electrically long-term stable in an aqueous electrolyte. The long-term stability was investigated and confirmed at elevated temperatures.

[0058] The manufacturing of the ruthenium oxide layers were conducted with a coating liquid consisting of a metal salt solved or dispersed in an organic solvent. After coating, the precursor substance was converted at temperatures between 360° C. and 500° C. The obtained RuOx-layers had a thickness in the range of 0.04 μm to 0.4 μm, and were fully crystalized, electrically conductive and mechanically very stable. In a second step, a paste containing activated carbon and a suitable binder was applied on the metal oxide coated titanium surface and tempered.

[0059] In this example, the ruthenium oxide layers were manufactured with a solution of 10 mmol/l to 200 mmol/l ruthenium (III) chloride hydrate in methanol. After coating the precursor was converted and annealed in a furnace at temperatures between 360° C. and 500° C. The obtained RuOx layers had a thickness in the range of 0.04 μm to 0.4 μm, were fully crystalized, electrically conductive and mechanically very stable. In a second step, a coating of activated carbon and PVDF in an organic solvent was applied on the metal oxide coated titanium surface and annealed at a temperature of 200° C.

[0060] FIGS. 2 and 3 show scanning electron microscopic images of nano-structured ruthenium oxide coated surfaces. In FIG. 2, the surface exhibits spherical and cylindrical structures or particles with an approx. size of 10 nm. As can be seen in FIG. 3, a different process control, in which a thicker ruthenium oxide layer was applied, resulted in a formation of nanowires that are larger than 50 nm. This structure is likewise porous. FIG. 4 shows a scanning electron microscopic image of a nano-structured iridium oxide coated surface.

[0061] FIG. 5 shows cyclic voltammograms of titanium substrates that have been coated with ruthenium oxide or iridium oxide as well as an uncoated substrate. While the uncoated titanium substrate becomes passivated upon anodic polarisation and even at higher depolarisation no current flows, both ruthenium and iridium oxide coated substrates remain active, while the current density remains stable without any passivation. The voltammograms have been obtained using a test electrolyte containing 120:80:30 (volume fractions) of ethylene glycol, water and acetic acid with 12 weight fractions of ammonium acetate and 10 mmol/l KCl. Voltages were determined in relation to an Ag/AgCl reference electrode.

[0062] It will be apparent to those skilled in the art that numerous modifications and variations of the described examples and embodiments are possible in light of the above teachings of the disclosure. The disclosed examples and embodiments are presented for purposes of illustration only. Other alternate embodiments may include some or all of the features disclosed herein. Therefore, it is the intent to cover all such modifications and alternate embodiments as may come within the true scope of this invention, which is to be given the full breadth thereof. Additionally, the disclosure of a range of values is a disclosure of every numerical value within that range, including the end points.