Electrolytic Solution for Capacitor ESR Stability
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Solution Overview
Problem
The increase in equivalent series resistance (ESR) over time in electrolytic capacitors with conductive separators due to the dedoping phenomenon, where dopant agents from the conductive polymer layer leach into the electrolytic solution, leading to decreased conductivity and energy loss.
Innovation Solution
An electrolytic solution with a specific molar ratio of acid to base components that is excessive in acid, which suppresses the dedoping phenomenon by maintaining a pH close to that of the anionized dopant agent, and the use of antioxidants to prevent oxidative deterioration, along with a component having a reduction potential of −1.6 to 0V to preferentially induce reduction reactions in the p-type doping conductive polymer layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conductive polymer layer containing dopant agent is formed on the separator surface to improve ESR characteristic, then electric conductivity is improved, but the dopant agent gradually leaches into the electrolytic solution causing ESR to increase over time
Solution Approach 1:
The patent changes the chemical composition parameters of the electrolytic solution by incorporating a carboxylic acid component with specific pKa value (2.0-5.0) and controlling the molar ratio between carboxylic acid and quaternary compound (1:0.95 to 1:0.05). This parameter optimization suppresses the dedoping phenomenon by creating a chemical environment that stabilizes the dopant agent in the conductive polymer layer, thereby preventing ESR increase over time while maintaining low initial ESR values.
Solution Approach 2:
The patent employs a composite electrolytic solution system combining multiple components: quaternary compound (amidine-based), carboxylic acid component, and cyclic carbonate chain component. This composite formulation creates synergistic effects where the carboxylic acid interacts with the dopant agent to prevent its leaching, while the quaternary compound provides high conductivity. The composite material approach resolves the contradiction between initial performance and long-term stability.
2Loss of energy
If high electric conductivity electrolytic solution is used to reduce energy loss, then ESR characteristic is improved, but it is insufficient to prevent ESR increase over time in capacitors with conductive separators
Solution Approach 1:
The patent optimizes the molecular structure parameters of the carboxylic acid component, specifically selecting acids with pKa values between 2.0 and 5.0. This parameter selection is critical because it determines the acid's ability to suppress dopant leaching without compromising electrolyte conductivity. The controlled pKa range ensures optimal balance between preventing dedoping (improving reliability) and maintaining low energy loss.
Solution Approach 2:
The carboxylic acid component acts as an intermediary substance between the conductive polymer layer and the bulk electrolytic solution. It mediates the interaction by creating a chemical environment at the interface that prevents dopant agent leaching. The carboxylic acid serves as a buffer that maintains the chemical stability of the dopant, thereby preventing the harmful dedoping phenomenon while allowing the electrolyte to maintain its high conductivity for low energy loss.
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 solution significantly reduces the ESR increase over time, enhancing the lifespan and reliability of the electrolytic capacitors by preventing dedoping and oxidative degradation, while maintaining excellent ESR characteristics.
Implementation Method 1
a dopant agent gradually comes out of the conductive polymer layer containing the dopant agent into the electrolytic solution (hereinafter also referred to a dedoping phenomenon)
Implementation Method 2
the use of antioxidants to prevent oxidative deterioration, along with a component having a reduction potential of −1.6 to 0V to preferentially induce reduction reactions in the p-type doping conductive polymer layer
Implementation Method 3
there has been proposed an electrolytic capacitor having a structure in which a conductive separator formed with a conductive polymer layer on its surface is interposed between a pair of electrodes
Data Source
AI summary
An electrolytic solution for use in an electrolytic capacitor including a capacitor element and a casing containing the capacitor element, the capacitor element including a pair of electrodes, and a conductive separator (E) which is formed with a conductive polymer layer (F) containing a dopant agent (H) on its surface and is interposed between the pair of electrodes, the conductive separator (E) and the pair of electrodes being rolled up in an overlapped state with each other, and spaces between the pair of electrodes being impregnated with the electrolytic solution, wherein an acid component (D) and a base component (C) as electrolytic components to be contained in the electrolytic solution are at such a molar ratio that the acid component (D) is excessive. By use of the electrolytic solution, increase in the ESR with the elapse of time in an electrolytic capacitor is suppressed.