US-20260128234-A1 - ALUMINUM OXIDE LAYER ON ANODE FOIL FOR ALUMINUM ELECTROLYTIC CAPACITOR

Abstract

A method of producing a capacitor electrode includes forming an oxide layer on a foil. The method also includes heating the foil to a target temperature so as to induce defects in the oxide layer. The target temperature is about 350° C. to 560° C. and the duration of heating the foil to the target temperature is less than 6 minutes. The oxide layer is reformed so as to generate a reformed oxide layer that is an aluminum oxide with a boehmite phase and a pseudo-boehmite phase.

Inventors

• Ralph Jason Hemphill
• Henry Buser
• Brian Smith
• Corina Geiculescu
• David Bowen

Assignees

• PACESETTER, INC.

Dates

Publication Date

20260507

Application Date

20260102

Claims (20)

1. 1 . A method of producing a capacitor electrode, the method comprising: forming an oxide layer on a foil; heating the foil to a target temperature so as to induce defects in the oxide layer, the target temperature being greater than or equal to about 350° C. and less than or equal to 560° C., a duration of heating the foil to the target temperature being less than or equal to about 6 minutes; and reforming the oxide layer into a reformed oxide layer that is an aluminum oxide with a boehmite phase and a pseudo-boehmite phase, and the oxide layer being reformed after the defects are induced.
2. 2 . The method of claim 1 , wherein the defects include cracks in the oxide layer.
3. 3 . The method of claim 1 , wherein heating the foil to the target temperature includes placing the foil in an oven.
4. 4 . The method of claim 3 , wherein an oven target temperature for the oven is greater than or equal to 350° C. and less than or equal to 560° C.
5. 5 . The method of claim 4 , wherein the foil is removed from the oven upon expiration of the duration of heating the foil to the target temperature.
6. 6 . The method of claim 1 , wherein the temperature of the foil does not decrease during the heating the foil to the target temperature.
7. 7 . The method of claim 1 , wherein the duration of heating the foil to the target temperature is less than 220 seconds.
8. 8 . The method of claim 1 , further comprising: at least partially drying a surface of the foil after forming the oxide layer on the foil and before heating the foil to the target temperature.
9. 9 . The method of claim 1 , wherein at least partially drying a surface of the foil includes blowing air on the surface of the foil.
10. 10 . The method of claim 1 , wherein a temperature of the air is between 28° C. and 100° C.
11. 11 . The method of claim 1 , further comprising: rinsing the foil before at least partially drying the surface of the foil and after forming the oxide layer on the foil.
12. 12 . The method of claim 1 , wherein reforming the oxide layer reduces the number of defects such that the reformed oxide layer has fewer defects than the oxide layer had after the defects were induced.
13. 13 . The method of claim 1 , wherein reforming the oxide layer includes immersing the foil in a solution; maintaining a target current between the immersed foil and the solution until a target voltage is reached; and discharging the immersed foil after the third target voltage is reached.
14. 14 . The method of claim 1 , wherein forming the oxide layer on the foil includes immersing the foil in a first solution and maintaining a target current between the immersed foil and the first solution until a first target voltage is reached and discharging the immersed foil after the first target voltage is reached; inducing the defects in the oxide layer includes heating the foil at a temperature sufficient to induce the defects in the oxide layer; and reforming the oxide layer includes immersing the foil in a second solution and maintaining a second target current between the immersed foil and the second solution until a second target voltage is reached and discharging the immersed foil after the second target voltage is reached.
15. 15 . The method of claim 14 , wherein the second target voltage is maintained until a desired leakage current between the immersed foil and the second solution is achieved.
16. 16 . The method of claim 14 , further comprising: removing the foil from the second solution; immersing the foil in a phosphate-containing solution after removing the foil from the second solution; removing the foil from the phosphate-containing solution; and rinsing the foil.
17. 17 . The method of claim 14 , wherein the first target voltage is greater than the second target voltage.
18. 18 . The method of claim 14 , wherein a difference between the first target voltage and the second target voltage is about 5 Volts (V).
19. 19 . The method of claim 14 , wherein the first target voltage is maintained until a first desired leakage current is achieved.
20. 20 . The method of claim 1 , wherein the amount of the boehmite phase in the reformed oxide layer is greater than the amount of the pseudo-boehmite phase in the reformed oxide layer.

Description

RELATED APPLICATIONS This Patent Application is a continuation of U.S. patent application Ser. No. 18/232,820, filed on Aug. 11, 2023, entitled “Aluminum Oxide Layer on Anode Foil for Aluminum Electrolytic Capacitor,” and incorporated herein in its entirety; and U.S. patent application Ser. No. 18/232,820 is a continuation-in-part of U.S. patent application Ser. No. 17/099,733, filed on Nov. 16, 2020, entitled “Aluminum Oxide Layer on Anode Foil for Aluminum Electrolytic Capacitor,”and incorporated herein in its entirety; and U.S. patent application Ser. No. 17/099,733 is a continuation of U.S. patent application Ser. No. 16/888,647, filed on May 29, 2020, issued as U.S. Pat. No. 10,872,731, entitled “Aluminum Oxide Layer on Anode Foil for Aluminum Electrolytic Capacitor,” and incorporated herein in its entirety; and U.S. patent application Ser. No. 16/888,647 is a continuation of U.S. patent application Ser. No. 15/996,219, filed on Jun. 1, 2018, issued as U.S. Pat. No. 10,707,024, entitled “Method of Forming an Aluminum Oxide Layer on Anode Foil for Aluminum Electrolytic Capacitor,” and incorporated herein in its entirety. FIELD OF THE INVENTION The present disclosure relates generally to the field of electrolytic capacitors and batteries. BACKGROUND Compact, high voltage capacitors are utilized as energy storage reservoirs in many applications, including implantable medical devices. These capacitors are required to have a high energy density, since it is desirable to minimize the overall size of the implanted device. This is particularly true of an Implantable Cardioverter Defibrillator (ICD), also referred to as an implantable defibrillator, since the high voltage capacitors used to deliver the defibrillation pulse can occupy as much as one third of the ICD volume. Implantable cardioverter defibrillators, such as those disclosed in U.S. Pat. No. 5,131,388, the disclosure of which is hereby incorporated herein by reference, typically use two electrolytic capacitors in series to achieve the desired high voltage for shock delivery. For example, an ICD may utilize two 350 to 400 volt electrolytic capacitors in series to achieve a voltage of 700 to 800 volts. Electrolytic capacitors are used in ICDs because they have the most nearly ideal properties in terms of size, reliability and ability to withstand relatively high voltage. Conventionally, such electrolytic capacitors include an etched aluminum foil anode, an aluminum foil or film cathode, and a kraft paper or fabric gauze separator impregnated with a solvent-based liquid electrolyte interposed between the anode and the cathode. While aluminum is the preferred metal for the anode plates, other metals such as tantalum, magnesium, titanium, niobium, zirconium and zinc may be used. A typical solvent-based liquid electrolyte may be a mixture of a weak acid and a salt of a weak acid, preferably a salt of the weak acid employed, in a polyhydroxy alcohol solvent. The electrolytic or ion-producing component of the electrolyte is the salt that is dissolved in the solvent. The entire laminate is rolled up into the form of a substantially cylindrical body, or wound roll, that is held together with adhesive tape and is encased, with the aid of suitable insulation, in an aluminum tube or canister. Connections to the anode and the cathode are made via tabs. Alternative flat constructions for aluminum electrolytic capacitors are also known, comprising a planar, layered stack structure of electrode materials with separators interposed therebetween, such as those disclosed in the above-mentioned U.S. Pat. No. 5,131,388. In ICDs, as in other applications where space is a critical design element, it is desirable to use capacitors with the greatest possible capacitance per unit volume. Since the capacitance of an aluminum electrolytic capacitor is provided by the anodes, a clear strategy for increasing the energy density in the capacitor is to minimize the volume taken up by the separators and cathodes and maximize the number of anodes. A multiple anode stack configuration requires fewer cathodes and paper separators than a single anode configuration and thus reduces the size of the device. A multiple anode stack consists of a number of units each consisting of, in series, a cathode, a paper separator, two or more anodes, a paper separator and a cathode, with neighboring units sharing the cathode between them, all placed within the capacitor case. The energy density of aluminum electrolytic capacitors is directly related to the surface area of the anodes generated in the electrochemical etching processes. Typical surface area increases are 40 to 1 and represent 30 to 40 million tunnels/cm2. An electrochemical widening step is used to increase the tunnel diameter after etching to ensure the oxide layer described below will not close off the tunnels. The high surface area foil is put through an oxidation process to grow a voltage supporting oxide layer with low leakage curren