Wet electrolytic capacitor containing a hydrogen protection layer
A wet electrolytic capacitor that contains a casing within which is positioned an anode formed from an anodically oxidized sintered porous body and a fluidic working electrolyte is provided. The casing contains a metal substrate over which is disposed a hydrogen protection layer that contains a plurality of sintered agglomerates formed from a valve metal composition. The present inventors have discovered that through careful selection of the relative particle size and distribution of the agglomerates, the resulting protection layer can effectively absorb and dissipate hydrogen radicals generated during use and/or production of the capacitor, which could otherwise lead to embrittlement and cracking of the metal substrate.
1. A wet electrolytic capacitor comprising a casing within which is positioned an anode formed from an anodically oxidized sintered porous body and a fluidic working electrolyte, the casing containing a metal substrate over which is disposed a hydrogen protection layer that contains a plurality of sintered valve metal agglomerates formed from a valve metal composition, wherein the agglomerates have an aggregate D50 size of about 100 micrometers or less and wherein no more than about 5% of the agglomerates having a size greater than 150 micrometers.
2. The wet electrolytic capacitor of claim 1 , wherein the agglomerates have an aggregate D50 size of from about 1 to about 80 micrometers.
3. The wet electrolytic capacitor of claim 1 , wherein no more than about 2% of the agglomerates have a size greater than 150 micrometers.
4. The wet electrolytic capacitor of claim 1 , wherein the agglomerates have an average primary particle size of from about 5 nanometers to about 20 micrometers.
5. The wet electrolytic capacitor of claim 1 , wherein the agglomerates have a specific surface area of about 1.2 m 2 /g or more.
6. The wet electrolytic capacitor of claim 1 , wherein the valve metal composition includes tantalum.
7. The wet electrolytic capacitor of claim 1 , wherein the metal substrate is formed from tantalum.
8. The wet electrolytic capacitor of claim 1 , wherein the agglomerates are sintered to the metal substrate.
9. The wet electrolytic capacitor of claim 1 , wherein the agglomerates have a specific charge of about 100,000 μF*V/g or more.
10. The wet electrolytic capacitor of claim 1 , further comprising an electrochemically active material that overlies the metal substrate.
11. The wet electrolytic capacitor of claim 10 , wherein the protection layer is positioned between the metal substrate and the electrochemically active material.
12. The wet electrolytic capacitor of claim 10 , wherein the electrochemically active material includes a conductive polymer.
13. The wet electrolytic capacitor of claim 1 , wherein the anode includes tantalum.
14. The wet electrolytic capacitor of claim 1 , wherein the working electrolyte is a liquid.
15. The wet electrolytic capacitor of claim 1 , wherein the working electrolyte is an aqueous solution containing sulfuric acid.
16. The wet electrolytic capacitor of claim 1 , wherein a dielectric layer is present on the metal substrate.
17. The wet electrolytic capacitor of claim 1 , wherein the casing defines an opening and a sidewall surrounding an interior, and wherein a sealing assembly covers the opening.
18. A method for forming the electrolytic capacitor of claim 1 , the method comprising:
sintering the agglomerates to the metal substrate;
positioning an anode within an interior of the casing; and
placing a fluid working electrolyte within the interior of the casing.
19. The method of claim 18 , wherein the metal substrate is anodically oxidized before the agglomerates are sintered thereto.