Wet electrolytic capacitor for use at high temperatures
A wet electrolytic capacitor that contains an anode formed from an anodically oxidized sintered porous body and a fluidic working electrolyte is provided. The casing contains a metal substrate coated an electrochemically-active material. Through a unique and controlled combination of features relating to the capacitor configuration and sealing assembly, the present inventor has discovered that good electrical properties (e.g., ESR stability) can be achieved at relatively high temperatures. One unique feature of the wet electrolytic capacitor that can help achieve such good ESR stability is the presence of a dielectric layer on the metal substrate of the cathode within a controlled thickness range. In other embodiments, a sealing assembly may be employed that contains a hermetic seal (e.g., glass-to-metal seal) and an elastomeric barrier seal formed from a high-temperature elastomeric material.
1. A wet electrolytic capacitor comprising:
a casing that defines an opening and a sidewall surrounding an interior, wherein the casing contains an anodically oxidized metal substrate having a dielectric layer with a thickness of from about 10 nanometers to about 500 nanometers, wherein the metal substrate is coated with an electrochemically active material;
an anode positioned within the interior of the casing, wherein the anode is formed from an anodically oxidized sintered porous body, the anode comprising an anode lead extending therefrom; and
a fluid working electrolyte that is in electrical contact with the anode and the electrochemically active material.
2. The wet electrolytic capacitor of claim 1 , further comprising a sealing assembly that covers the opening and includes a hermetic seal and a barrier seal, wherein the barrier seal contains an elastomeric material.
3. The wet electrolytic capacitor of claim 2 , wherein the elastomeric material includes a perfluoroelastomer.
4. The wet electrolytic capacitor of claim 2 , wherein the elastomeric material exhibits an elongation at break of about 100% or more and/or a tensile strength at break of about 2 Megapascals or more at a temperature of 200° C., as determined in accordance with ASTM D412 at a tensile grip speed of 500 millimeters per minutes.
5. The wet electrolytic capacitor of claim 1 , wherein the thickness of the dielectric layer is from about 20 to about 100 nanometers.
6. The wet electrolytic capacitor of claim 1 , wherein the metal substrate is formed from tantalum.
7. The wet electrolytic capacitor of claim 1 , wherein the metal substrate forms all or a part of the casing.
8. The wet electrolytic capacitor of claim 1 , wherein the electrochemically active material includes sintered tantalum particles, conductive polymer, or a combination thereof.
9. The wet electrolytic capacitor of claim 1 , wherein the anode includes tantalum.
10. The wet electrolytic capacitor of claim 2 , further comprising a conductive tube that extends through the hermetic seal and/or the barrier seal, wherein the anode lead extends through the conductive tube.
11. The wet electrolytic capacitor of claim 10 , further comprising an external positive lead that is sealed at an end of the conductive tube and an external negative lead that is sealed to a lower wall of the casing.
12. The wet electrolytic capacitor of claim 2 , wherein the barrier seal is in contact with the hermetic seal.
13. The wet electrolytic capacitor of claim 12 , wherein the barrier seal covers a substantial portion of a surface of the hermetic seal.
14. The wet electrolytic capacitor of claim 1 , wherein the metal substrate is anodically oxidized by placing the substrate in an electrolyte bath and passing a current therethrough.
15. The wet electrolytic capacitor of claim 14 , wherein the current is applied at a forming voltage of from about 7 volts to about 25 volts.
16. The wet electrolytic capacitor of claim 14 , wherein the current is applied at a voltage of from about 12 to about 22 volts.
17. The wet electrolytic capacitor of claim 1 , wherein the wet electrolytic capacitor exhibits an equivalence series resistance of about 3,000 milliohms or less at a temperature of 200° C., measured with a 2-volt bias and 1-volt signal at a frequency of 120 Hz.
18. The wet electrolytic capacitor of claim 1 , wherein the thickness of the dielectric layer is from about 30 nanometers to about 80 nanometers.