Wound Electric Double-Layer Capacitor Asymmetric Electrode Design
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Solution Overview
Problem
Conventional wound electric double-layer capacitors experience electrochemical reactions at the surface of polarized electrode layers, leading to characteristic degradation such as gas generation, resistance increase, and capacity reduction due to unequal polarization and electrolyte interactions, causing separator degradation.
Innovation Solution
The capacitors are designed with polarized electrode layers wound an extra turn on the negative electrode, positioning these layers on the outermost surface and ensuring no polarized layers face the coupling parts through the separator, maintaining the potential in an electrochemically stable region to prevent electrolyte anion concentration and alkaline component attraction, thus reducing electrochemical reactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polarized electrode layers are formed on both surfaces of current collectors and wound together, then the capacitor structure is complete and functional, but electrochemical reactions occur at the surface leading to characteristic degradation
Solution Approach 1:
The harmful polarized electrode layer is extracted from the outermost surface of the wound capacitor element. By making the negative electrode longer than the positive electrode, the polarized electrode layer of the positive electrode is excluded from the outermost surface, eliminating the site where electrochemical reactions occur while maintaining the functional integrity of the capacitor structure
Solution Approach 2:
The capacitor structure employs asymmetric electrode lengths where the negative electrode extends beyond the positive electrode. This asymmetry ensures that the polarized electrode layer is not present on the outermost surface, preventing electrochemical reactions while maintaining electrical functionality through proper winding configuration
2Reliability
If the capacitor operates with standard electrode configuration, then it provides normal capacitance function, but gas generation and resistance increase occur due to electrochemical reactions
Solution Approach 1:
The harmful polarized electrode layer is extracted from the outermost surface by extending the negative electrode beyond the positive electrode. This removal prevents electrochemical reactions that cause gas generation and resistance increase, while the capacitor maintains its normal capacitance function through the internal electrode structure
3Reliability
If polarized electrode layers are present on the outermost surface, then the capacitor structure is symmetric and simple, but separator degradation occurs due to electrolyte anion concentration and alkaline component attraction
Solution Approach 1:
The polarized electrode layer is extracted from the outermost surface where it would interact with electrolyte anions and alkaline components. By making the negative electrode longer, the positive electrode's polarized layer is excluded from the surface, preventing separator degradation while maintaining the capacitor's functional structure
Solution Approach 2:
The outermost surface of the capacitor is effectively created as an inert environment by excluding the reactive polarized electrode layer. The extended negative electrode creates a surface configuration that prevents harmful electrolyte interactions, protecting the separator from degradation
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 design significantly reduces characteristic degradation, maintaining high reliability by preventing gas generation, resistance increase, and capacity reduction, while ensuring the separator does not degrade.
Implementation Method 1
maintaining the potential in an electrochemically stable region to prevent electrolyte anion concentration and alkaline component attraction
Implementation Method 2
a capacitor element formed by winding a positive electrode and a negative electrode while a separator is interposed between them
Data Source
AI summary
A wound electric double-layer capacitor suppresses electrochemical reaction on polarized electrode layers, reduces characteristic degradation, and has high reliability. The capacitor has a capacitor element formed by winding positive and negative electrodes with a separator interposed between them, a metal case for storing the capacitor element and an electrolyte for driving, and a sealing member for sealing an opening of the metal case. In the positive and negative electrodes, positive and negative electrode lead wires are coupled to exposed parts of current collectors having polarized electrode layers on their both surfaces, respectively. The negative electrode is wound at least one extra turn from the winding end of the positive electrode of the capacitor element, and hence a part where the polarized electrode layers formed in the negative electrode face each other through the separator is formed on the outermost periphery of the capacitor element.