CN-122029625-A - Alumina layer on anode foil of aluminum electrolytic capacitor

Abstract

A method of manufacturing a capacitor electrode includes forming an oxide layer on a foil. The method further includes heating the foil to a target temperature to induce defects in the oxide layer. The target temperature is about 450 ℃ to 560 ℃ and the duration of heating the foil to the target temperature is less than 4 minutes. The oxide layer is reformed so as to produce a reformed oxide layer that is alumina having a boehmite phase and a pseudo-boehmite phase.

Inventors

• R. J. Hemp Hill
• H Brussels
• J.B. SMITH
• C. Jikelescu
• D. Bao Wen

Assignees

• 先导者股份有限公司

Dates

Publication Date

20260512

Application Date

20240806

Priority Date

20230811

Claims (20)

1. 1. A method of manufacturing a capacitor electrode, the method comprising: Forming an oxide layer on the foil; heating the foil to a target temperature, so as to induce defects in the oxide layer, The target temperature is greater than or equal to about 450 ℃ and less than or equal to 560 ℃, Heating the foil to the target temperature for a duration of less than or equal to about 4 minutes, and Reforming the oxide layer into a reformed oxide layer, the reformed oxide layer being alumina having a boehmite phase and a pseudo-boehmite phase, and The oxide layer is reformed after the defect is induced.
2. 2. The method of claim 1, wherein the defect comprises a crack in the oxide layer.
3. 3. The method of claim 1, wherein heating the foil to the target temperature comprises placing the foil in an oven.
4. 4. A method according to claim 3, wherein the oven target temperature for the oven is greater than or equal to 450 ℃ and less than or equal to 560 ℃.
5. 5. The method of claim 4, wherein the foil is removed from the oven once the duration of heating the foil to the target temperature expires.
6. 6. The method of claim 1, wherein the temperature of the foil does not decrease during heating of 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 the surface of the foil comprises blowing air against the surface of the foil.
10. 10. The method of claim 1, wherein the temperature of the air is between 28 ℃ and 100 ℃.
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 an oxide layer after the defects are induced.
13. 13. The method of claim 1, wherein reforming the oxide layer comprises immersing the foil in a solution; maintaining a target current between the immersed foil and the solution until a target voltage is reached, and After reaching a third target voltage, the immersed foil is discharged.
14. 14. The method of claim 1, wherein forming the oxide layer on the foil comprises 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 defect in the oxide layer includes heating the foil to a temperature sufficient to induce the defect 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 is achieved between the immersed foil and the second solution.
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 The foil is rinsed.
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 content of the boehmite phase in the reformed oxide layer is greater than the content of the pseudo-boehmite phase in the reformed oxide layer.

Description

Alumina layer on anode foil of aluminum electrolytic capacitor RELATED APPLICATIONS This patent application claims priority from U.S. patent application Ser. No. 18/232,820, entitled "Aluminum Oxide Layer on Anode Foil for Aluminum Electrolytic Capacitor," filed 8/11 at 2023, and incorporated herein in its entirety. Technical Field The present disclosure relates generally to the field of electrolytic capacitors and batteries. Background Compact high voltage capacitors are used as energy storage devices in many applications, including implantable medical devices. These capacitors are required to have high energy density because it is desirable to minimize the overall size of the implantable device. This is particularly important for implantable cardioverter defibrillators (Implantable Cardioverter Defibrillator, ICD, also known as implantable defibrillators) because the high voltage capacitors used to deliver the defibrillation pulses can occupy up to one third of the volume of the ICD. Implantable Cardioverter Defibrillators (ICDs), such as the ICD disclosed in U.S. patent No. 5,131,388, the disclosure of which is incorporated herein by reference, typically use two electrolytic capacitors in series to achieve the desired high voltage for delivering a shock. For example, an ICD may utilize two electrolytic capacitors in series of 350 to 400 volts to achieve a voltage of 700 to 800 volts. Electrolytic capacitors are used in ICDs because of their most desirable characteristics in terms of size, reliability, and ability to withstand relatively high voltages. Traditionally, such electrolytic capacitors include etched aluminum foil anodes, aluminum foil or thin film cathodes, and kraft paper or textile gauze separators impregnated with a solvent-based liquid electrolyte between the anode and cathode. While aluminum is the preferred metal for the anode plate, other metals such as tantalum, magnesium, titanium, niobium, zirconium, and zinc may also be used. A typical solvent-based liquid electrolyte may be a mixture of a weak acid and a weak acid salt (preferably the salt of the weak acid employed) in a polyhydric alcohol solvent. The electrolytic or ion-generating component of the electrolyte is a salt dissolved in a solvent. The entire laminate is rolled into the form of a substantially cylindrical body or roll which is secured together with tape and is enclosed in an aluminium tube or can by means of a suitable insulating material. The connection of the anode and cathode is via tabs. Alternative flat structures for aluminum electrolytic capacitors are also known, which include planar laminated structures of electrode materials with separators interposed therebetween, such as the structure disclosed in the above-mentioned U.S. patent No. 5,131,388. In ICDs, as in other applications where space is a critical design element, it is desirable to use capacitors having as high a capacitance per unit volume as possible. Since the capacitance of aluminum electrolytic capacitors is provided by the anodes, a clear strategy for increasing the energy density of the capacitor is to minimize the volume occupied by the separator and cathode and maximize the number of anodes. The multi-anode stacked configuration requires fewer cathodes and paper separators than the single-anode configuration, thereby reducing the size of the apparatus. The multi-anode stack is made up of a plurality of cells, each cell being made up of a cathode, a paper separator, two or more anodes, a paper separator and a cathode in series, adjacent cells sharing the cathode therebetween, all of the cells being placed within the capacitor housing. The energy density of an aluminum electrolytic capacitor is directly related to the surface area of the anode generated in the electrochemical etching process. Typical surface area increases are 40:1, corresponding to 3000 to 4000 thousand tunnels per square centimeter. After etching, an electrochemical diameter expansion step is used to increase the tunnel diameter to ensure that the oxide layer described below does not block the tunnel. The high surface area foil is subjected to an oxidation process to grow a pressure resistant oxide layer having low leakage current and low deformation characteristics. After the oxidation process, an oven depolarization process is used to drive off the hydration water, induce stress cracking and expose the weak areas. Subsequent oxidation processes (i.e., reforming processes), "repair" the stress crack and improve the resulting leakage current. The number of defects may decrease with each subsequent reforming and depolarization process until a stable defect level is achieved. However, the inventors have found that the use of multiple depolarization steps has a negative impact on the capacitance and deformation of the electrolytic capacitor. Accordingly, there is a need in the art for improved oxide formation processes. Disclosure of Invention Disclosed herein are metal foils havi