ALD-Coated Porous Cathode Foil for Low-ESR Capacitors
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Solution Overview
Problem
Existing cathode foils for electrolytic capacitors face challenges in maintaining high capacitance and low equivalent series resistance (ESR) due to degradation issues caused by reactions with the electrolyte, especially when the electrolyte contains moisture.
Innovation Solution
A cathode foil design incorporating a metal porous part with open pores at one main surface, a continuous metal core part, and a coating film formed using the atomic layer deposition (ALD) method, which includes a conductive first layer and/or an oxide second layer, and optionally a third layer containing phosphorus or nitrogen to enhance solvent resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a roughened metal foil or anodized foil is used as cathode body to increase capacitance, then the electrostatic capacitance is improved, but the cathode foil degrades due to reactions with electrolyte containing moisture
Solution Approach 1:
A coating film is introduced as an intermediary layer between the metal porous part and the electrolyte. This coating film acts as a protective barrier that prevents direct contact and chemical reactions between the metal cathode and moisture-containing electrolyte, thereby improving water resistance while preserving capacitance
Solution Approach 2:
The cathode structure is designed as a composite material system combining metal porous part with coating film. This composite structure integrates the high capacitance properties of porous metal with the protective properties of the coating film, achieving both high capacitance and improved water resistance
2Quantity of substance
If the cathode foil surface is roughened to increase capacitance, then the electrostatic capacitance is improved, but the equivalent series resistance (ESR) increases due to degradation
Solution Approach 1:
The coating film serves as a protective intermediary that prevents degradation of the metal porous part. By blocking the interaction between electrolyte moisture and the metal surface, the coating film prevents the formation of high-resistance degradation products, thereby maintaining low ESR while preserving the high-capacitance porous structure
Solution Approach 2:
The coating film is formed on the cathode foil before assembly into the capacitor. This preliminary protective action prevents degradation from occurring during capacitor operation, ensuring that the cathode maintains its low ESR characteristics throughout the product lifecycle
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
The proposed cathode foil structure improves the characteristics of electrolytic capacitors by enhancing capacitance on the cathode side, reducing ESR, and providing excellent water resistance and withstand voltage, thus mitigating degradation issues.
Implementation Method 1
The coating film is formed by an atomic layer deposition (ALD) method
Data Source
AI summary
A cathode foil for electrolytic capacitors includes a metal porous part, a metal core part that is continuous with the metal porous part, and a coating film covering the metal porous part. Pores in the metal porous part are open at a first main surface of the cathode foil. The coating film is disposed in a region from the first main surface to a depth more than or equal to 10% of a thickness of the metal porous part in a thickness direction of the metal porous part.