Electrochemical Drilling for Anode Foil Porosity
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Solution Overview
Problem
Existing methods for creating porous anode foils in multiple anode stack configurations for implantable cardioverter defibrillators result in high equivalent series resistance (ESR), which reduces charge efficiency and increases production downtime due to aluminum hydroxide precipitation in neutral pH electrochemical drilling solutions.
Innovation Solution
An electrochemical drilling system and process using an acidic ECD solution with a pH of less than 5, where the solution is replenished and circulated to maintain a steady state concentration of dissolved aluminum, preventing precipitation and reducing the need for frequent solution renewal and caustic cleaning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a multiple anode stack configuration is used to increase energy density, then capacitance per unit volume increases, but equivalent series resistance increases due to tortuous conduction paths
Solution Approach 1:
The patent applies porous anode foil with controlled pore structures to create direct conduction pathways through the anode layers. The pores allow charge to flow directly from cathode to inner anodes without following tortuous paths through outer anodes, thereby reducing equivalent series resistance while maintaining the high capacitance density provided by the multiple anode stack configuration.
Solution Approach 2:
The patent introduces a new dimensional pathway through the anode structure by creating through-pores that extend in the thickness direction of the anode foil. This dimensional change transforms the conduction path from a two-dimensional tortuous surface path to a three-dimensional direct through-path, enabling shorter and more efficient charge transport routes.
2Manufacturing precision
If neutral pH electrochemical drilling solution is used, then aluminum hydroxide precipitates forming in the solution, but this causes frequent solution renewal and caustic cleaning which increases production downtime
Solution Approach 1:
The patent changes the pH parameter of the electrochemical drilling solution from neutral to acidic (pH less than 5). This parameter change prevents aluminum hydroxide precipitation by maintaining aluminum in its dissolved ionic form in the acidic environment, thereby eliminating the need for frequent solution renewal and caustic cleaning operations while still achieving the desired electrical porosity in the anode foil.
Solution Approach 2:
The patent converts the potentially harmful effect of aluminum dissolution during electrochemical drilling into a beneficial outcome. By using acidic pH, the dissolved aluminum remains in solution rather than precipitating as hydroxide, and the aluminum ions themselves can participate in the electrochemical reactions to enhance pore formation and electrical porosity, turning a waste product into a useful component of the process.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces ESR, maintains high capacitance, and minimizes production downtime by preventing aluminum hydroxide formation, ensuring consistent electrical porosity and charge efficiency in the anode foils.
Implementation Method 1
a method for creating porous anode foils includes electrochemical drilling a plurality of etched metal foils in sequence one after the other, in a bath containing an electrochemical drilling (ECD) solution
Implementation Method 2
an acidic ECD solution with a pH of less than 5, where the solution is replenished and circulated to maintain a steady state concentration of dissolved aluminum, preventing precipitation
Data Source
AI summary
A process for creating porous anode foil for use in an electrolytic capacitor of an implantable cardioverter defibrillator is provided. The process includes electrochemical drilling a plurality of etched metal foils in sequence one after the other in a bath containing electrochemical drilling (ECD) solution initially having a pH of less than 5. Alternatively, an etched foil sheet may be passed through the bath in a substantially continuous manner such that a portion of said etched foil sheet is in contact with the ECD solution is electrochemically drilled to generate pores. Electrochemical drilling is achieved when a current is passed to the foil or portion of the foil sheet in solution, ECD replenishment solution having a pH of less than about 5 is added from a feed reservoir to the bath at such a rate so as to maintain a pH in the ECD solution in the bath of less than about 5, and ECD solution in the bath is removed to a waste reservoir at the substantially the same rate as the addition of the ECD replenishment solution to the bath.