Solid Electrolytic Capacitor Separator for High-Temperature ESR Stability
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Solution Overview
Problem
Solid electrolytic capacitors experience a significant increase in Equivalent Series Resistance (ESR) when exposed to high-temperature environments due to the reaction between the cellulose fiber separator and the acid-doped conductive polymer, leading to the separation of the conductive path.
Innovation Solution
Using a cellulose fiber separator treated with alkali to reduce the number of hydroxyl groups, preventing the attachment of the carbon layer and minimizing the hydrolysis of the 1,4-glycosidic bonds, thus maintaining the integrity of the conductive path even at high temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a carbon layer is formed on the surface of the cathode foil to reduce ESR, then the adhesion between the carbon layer and conductive polymer improves, but the oxide film gradually grows on the surface of the metal carbide at high temperatures
Solution Approach 1:
The patent removes the problematic metal carbide layer from the cathode foil surface and replaces it with a carbon layer formed by dry plating. This extraction eliminates the oxide film growth issue while maintaining the low ESR benefit through the carbon layer's adhesion to the conductive polymer.
Solution Approach 2:
The patent changes the material parameter of the cathode surface from metal carbide to carbon (formed by dry plating). This parameter change prevents oxide film growth at high temperatures while maintaining the electrical conductivity and adhesion properties needed for low ESR.
2Strength
If cellulose fiber separator is used to hold the conductive polymer, then the separator provides good structural support, but the hydroxyl groups in cellulose fiber react with acid components at high temperatures causing conductive path separation
Solution Approach 1:
The patent applies alkali treatment to the cellulose fiber separator, which removes the harmful hydroxyl groups that cause high-temperature reactions. This conversion transforms the separator into a material that maintains its structural support function while eliminating the chemical reactivity that leads to conductive path separation.
Solution Approach 2:
The patent changes the chemical composition parameter of the cellulose fiber by treating it with alkali. This parameter change reduces the hydroxyl group content, preventing the hydrolysis reaction with acid-doped conductive polymer at high temperatures while preserving the fiber's mechanical strength.
3Temperature
If the solid electrolytic capacitor is exposed to high-temperature environment, then the operational temperature range is extended, but the ESR significantly increases due to hydrolysis reaction
Solution Approach 1:
The patent applies alkali treatment to the cellulose fiber separator in advance, before the capacitor is exposed to high temperatures. This preliminary action removes the hydroxyl groups that would otherwise react with the acid-doped conductive polymer, preventing the hydrolysis reaction and ESR increase when the capacitor operates at high temperatures.
Solution Approach 2:
The patent performs dry plating to form a carbon layer on the cathode foil surface before assembly. This preliminary action creates a stable, non-reactive surface that prevents oxide film growth during high-temperature operation, ensuring long-term ESR stability.
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 ESR of the solid electrolytic capacitor is suppressed under high-temperature conditions, ensuring consistent performance by preventing the separation of the conductive path.
Implementation Method 1
the cellulose fiber easily adheres to the carbon layer due to hydrogen bonding between the hydroxyl groups of each other
Implementation Method 2
when this 1,4-glycosidic bond reacts with the acid component doped to the conductive polymer, the bonds between the cellulose fiber is dissolved by hydrolysis reaction
Implementation Method 3
By forming a carbon layer on the surface of the cathode foil, the formation of the oxide film at the cathode side is prevented
Data Source
Figure 1~2
Figure 3~4
Figure 5A~5C
AI summary
An electrolytic capacitor in which an increase in the ESR is suppressed even under the high-temperature environment is provided. The electrolytic capacitor includes anode foil, a cathode body, a separator, and a solid electrolyte layer. The anode foil is formed of valve metal and has dielectric oxide film on a surface of the foil. The cathode body includes cathode foil formed of valve metal and a carbon layer laminated on the cathode foil. The solid electrolyte layer includes conductive polymers held in the separator and is doped with acid components. The separator includes fiber, which has hydroxyl groups and in which molecules are bonded by 1,4-glycosidic bond, treated with alkali.