EDLC Binder Expansion Control in γ-Butyrolactone
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Solution Overview
Problem
Electric double-layer capacitors with coated electrodes using γ-butyrolactone as a solvent face significant internal resistance increases at elevated temperatures, limiting their operational range to 60°C due to binder expansion issues, which worsens at 85°C.
Innovation Solution
Employing a coated electrode with a styrene-butadiene elastomer binder that has an expansion rate of 50% or less in γ-butyrolactone at 85°C, and using an electrolyte solution with a fluorine-containing anion, along with a current collector with reduced water content and a conductive coating layer, to mitigate internal resistance changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a coated electrode with acrylic elastomer binder is used in γ-butyrolactone electrolyte solution, then the capacitor can operate at elevated temperatures, but the internal resistance increases significantly due to binder expansion
Solution Approach 1:
The patent changes the chemical composition parameter of the binder from acrylic elastomer to styrene-butadiene elastomer, which has fundamentally different swelling characteristics in γ-butyrolactone. This parameter change transforms the binder's expansion behavior at elevated temperatures, resolving the contradiction between temperature capability and resistance stability.
Solution Approach 2:
The patent creates a composite electrode structure where styrene-butadiene elastomer binder is combined with activated carbon and conductive auxiliary agents. This composite material system provides both the mechanical binding function and the thermal stability required for high-temperature operation in γ-butyrolactone electrolyte solutions.
2Reliability
If the binder expansion is suppressed to maintain low internal resistance, then the electrode structure stability improves, but the binding agent effectiveness may be compromised
Solution Approach 1:
The patent modifies the binder's chemical structure by selecting styrene-butadiene elastomer with specific molecular characteristics that provide both low expansion in γ-butyrolactone and adequate binding strength. The parameter change in elastomer type resolves the contradiction between suppression of expansion and maintenance of binding effectiveness.
3Ease of manufacture
If conventional acrylic elastomer binder is used, then the electrode can be manufactured easily, but the capacitor cannot maintain performance at temperatures above 60°C
Solution Approach 1:
The patent changes the binder material parameter from acrylic elastomer to styrene-butadiene elastomer, which maintains the ease of manufacturing through similar coating processes while fundamentally improving the temperature performance. The new elastomer type allows operation up to 85°C without performance 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
The solution effectively suppresses the expansion of the binding agent, reducing internal resistance changes and enhancing the long-term reliability of electric double-layer capacitors, allowing them to operate effectively up to 85°C.
Implementation Method 1
a styrene-butadiene elastomer having an expansion rate of 50% or less in γ-butyrolactone at 85°C after 100 hours
Implementation Method 2
an electrolyte solution with a fluorine-containing anion
Implementation Method 3
a current collector with reduced water content
Data Source
Figure 1~1(C)
Figure 2~2(B)
Figure 3
AI summary
The electric double-layer capacitor of the present invention comprises an electrolyte solution comprising γ-butyrolactone as the solvent and acoated electrode. The coated electrodeis produced by using water as the solvent, and prepared by coating a slurry onto a current collector, wherein the slurry consists of an electrode material which is the solute, an electrically conductive auxiliary agent, and an elastomer having an expansion rate of 50% or less in γ-butyrolactone at 85°C after 100 hours as the binding agent.For example, a styrene-butadiene elastomer is employed as the elastomer. Because expansion ratein γ-butyrolactone is low, deterioration of internal resistance does not occur. Styrene-butadiene elastomer is easy to handle since water can be used as the solvent for the slurry.