Electric Double-Layer Capacitor Electrolyte Stability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Electric double-layer capacitors face challenges in maintaining high capacitance and low internal resistance while withstanding low-temperature, high-voltage, and high-temperature environments, as existing solutions either break down or exhibit increased internal resistance due to solvent degradation or electrolyte instability.
Innovation Solution
The use of an electrolytic solution comprising spirobipyrrolidinium tetrafluoroborate as the electrolyte and a solvent mixture of 50-60% propylene carbonate, 30-36% dimethyl carbonate, and 4-20% ethyl methyl carbonate, which maintains initial performance and minimizes characteristic changes across varying environmental conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ethylene carbonate is used as the solvent to promote dissociation and improve internal resistance, then low-temperature characteristics improve, but the solvent breaks down at high temperatures above 2.5V causing capacitor deterioration
Solution Approach 1:
The patent uses a composite solvent system combining propylene carbonate (50-60 vol%), dimethyl carbonate (30-36 vol%), and ethyl methyl carbonate (4-20 vol%). This composite approach leverages the high dielectric constant of propylene carbonate for good dissociation, while the carbonate components provide thermal stability and suppress decomposition at high temperatures above 2.5V, resolving the contradiction between low-temperature performance and high-temperature stability.
Solution Approach 2:
The patent changes the physical and chemical parameters of the solvent system by selecting specific components with complementary properties. Propylene carbonate provides high dielectric constant for ion dissociation, while dimethyl carbonate and ethyl methyl carbonate contribute to lower viscosity and higher thermal stability, allowing the electrolyte to maintain performance across wide temperature ranges from -40°C to 85°C.
2Reliability
If imidazolium salt is used as electrolyte to resist depositing at low temperatures, then low-temperature characteristics improve, but withstand voltage is not high enough and electrolyte breaks down above 2.5V
Solution Approach 1:
The patent changes the chemical structure parameter of the electrolyte by using spirobipyrrolidinium salt instead of imidazolium salt. The spirobipyrrolidinium cation structure provides higher charge delocalization and electrochemical stability, enabling the electrolyte to withstand voltages above 2.5V without decomposition while maintaining good low-temperature performance.
3Reliability
If quaternary ammonium hexafluorophosphate is used as electrolyte to improve dissociation property, then low-temperature characteristics improve, but heat resistance and water resistance are low causing reaction with trace water at high temperature
Solution Approach 1:
The patent changes the anion parameter by using tetrafluoroborate (BF4-) instead of hexafluorophosphate (PF6-). The tetrafluoroborate anion provides sufficient dissociation for good low-temperature performance while offering superior thermal stability and water resistance, preventing reactions with trace water even at high temperatures up to 85°C.
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 configuration ensures that the electric double-layer capacitor retains its initial high capacitance and low internal resistance, with minimal characteristic changes when exposed to low-temperature, high-voltage, or high-temperature environments, outperforming prior art in stability and performance.
Implementation Method 1
use of ethylene carbonate as the solvent of electrolytic solution promotes the dissociation of electrolytic solution due to the high dielectric constant of the solvent
Implementation Method 2
the solute is imidazolium salt, wherein the electrolytic solution does not deposit, solidify, etc., even at extremely low temperatures
Data Source
AI summary
An electric double-layer capacitor contains an electrolytic solution, wherein the electrolytic solution comprises 1.2 to 1.8 mol/L of spirobipyrrolidinium tetrafluoroborate as electrolyte as well as solvent, where the solvent contains 50 to 60 percent by volume of propylene carbonate, 30 to 36 percent by volume of dimethyl carbonate, and 4 to 20 percent by volume of ethyl methyl carbonate. The electric double-layer capacitor can maintain its initial high capacitance and low internal resistance, while undergoing smaller characteristic changes after being exposed to low-temperature environments, high-voltage environments or high-temperature environments.