Capacitor anode formed from flake powder
A capacitor anode that is formed from flake powder is provided. The anodes are formed from low density flake powder (e.g., relatively large in size), which is believed to provide a short transmission line between the outer surface and interior of the anode. This may result in a low equivalent series resistance (“ESR”) and improved volumetric efficiency for capacitors made from such anodes.
1. An electrolytic capacitor comprising an anode that is formed from a tantalum powder that is milled and thereafter compressed into the shape of the anode, the milled powder containing flakes having a bulk density of from about 0.2 to 0.6 grams per cubic centimeter, a specific surface area of from about 0.5 to about 10 meters squared per gram, and an aspect ratio of from about 2 to about 400, wherein a wire having a longitudinal axis is embedded within the powder and the flakes are generally oriented in a direction of the longitudinal axis of the wire and disposed in close contact therewith, and wherein the electrolytic capacitor exhibits an equivalent series resistance (“ESR”) of less than about 300 milliohms, measured with a 2-volt bias and 1-volt signal at a frequency of 2 MHz.
2. The electrolytic capacitor of claim 1 , wherein the flakes have a specific surface area of from about 2.0 to about 4.0 meters squared per gram.
3. The electrolytic capacitor of claim 1 , wherein the flakes have an aspect ratio of from about 10 to about 300.
4. The electrolytic capacitor of claim 1 , wherein the flakes have a screen size distribution of at least about 60 mesh.
5. The electrolytic capacitor of claim 1 , wherein the flakes have a screen size distribution of from about 60 mesh to about 325 mesh.
6. The electrolytic capacitor of claim 1 , wherein the anode has a density of from about 4.5 to about 6 grams per cubic centimeter.
7. The electrolytic capacitor of claim 1 , wherein the density of the anode is greater at a region adjacent to the anode wire than another region of the anode.
8. The electrolytic capacitor of claim 1 , wherein the capacitor has an equivalent series resistance of less than about 200 milliohms at a frequency of 2 Megahertz.
9. The electrolytic capacitor of claim 1 , wherein the capacitor has a dissipation factor of less than about 5% at a frequency of 2 Megahertz.
10. The electrolytic capacitor of claim 1 , further comprising a dielectric overlying the anode.
11. The electrolytic capacitor of claim 10 , further comprising a cathode overlying the dielectric layer.
12. The electrolytic capacitor of claim 11 , wherein the cathode comprises one or more conductive polymers.
13. The electrolytic capacitor of claim 11 , wherein the cathode comprises manganese dioxide.