Ultracapacitor High Temperature Stability
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Solution Overview
Problem
Conventional ultracapacitors are sensitive to high temperatures, leading to reduced capacitance and increased equivalent series resistance (ESR), necessitating a solution for maintaining stable electrical properties at elevated temperatures.
Innovation Solution
An ultracapacitor design featuring a first and second electrode with carbonaceous coatings on conductive metal current collectors, separated by a cellulosic fibrous separator and immersed in a nonaqueous electrolyte containing an ionic liquid, which maintains capacitance and low ESR even at temperatures above 80°C.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional ultracapacitors are used, then large capacitance values are achieved, but capacitance decreases and ESR increases at high temperatures
Solution Approach 1:
The patent changes the chemical composition parameters of the electrolyte by using ionic liquids with specific cations (imidazolium, pyridinium, pyrrolidinium, piperidinium, quaternary ammonium) and anions (halides, tetrafluoroborate, hexafluorophosphate, bis(trifluoromethylsulfonyl)imide) combined with nonaqueous solvents (cyclic carbonates, chain carbonates, carboxylic esters, nitriles, amides, sulfur compounds). This parameter change enables the electrolyte to maintain stable ionic conductivity and electrochemical stability at high temperatures up to 80°C or higher, resolving the contradiction between reliability and temperature range.
Solution Approach 2:
The patent employs composite materials throughout the ultracapacitor structure: carbonaceous coatings (activated carbon, carbon nanotubes, graphite) on current collectors, cellulosic fibrous separators, and composite electrolytes combining ionic liquids with nonaqueous solvents. These composite materials provide thermal stability, mechanical integrity, and electrochemical performance that maintain capacitance and low ESR at elevated temperatures, thereby improving reliability across a broader temperature range.
2Temperature
If high temperature operation is enabled, then extended operating range is achieved, but capacitance stability deteriorates
Solution Approach 1:
The patent changes the electrolyte composition parameters by selecting ionic liquids with appropriate viscosity, electrochemical stability, and thermal properties, combined with nonaqueous solvents that have high boiling points and good solvating ability. This parameter optimization ensures that the electrolyte maintains stable ionic conductivity and does not decompose at high temperatures, thereby maintaining capacitance stability while enabling extended operating temperature ranges.
Solution Approach 2:
The patent uses carbonaceous materials such as activated carbon particles, carbon nanotubes, and graphite, which are relatively inexpensive and provide excellent electrochemical stability and surface area for charge storage. These materials maintain their structural integrity and electrochemical properties at high temperatures, ensuring capacitance stability without requiring expensive specialized materials.
3Temperature
If high temperature operation is enabled, then extended operating range is achieved, but ESR increases
Solution Approach 1:
The patent changes the electrolyte parameters by using ionic liquids with low viscosity and high ionic conductivity, combined with nonaqueous solvents that enhance ion mobility. This parameter change reduces the equivalent series resistance (ESR) of the ultracapacitor and maintains low ESR at high temperatures by ensuring rapid ion transport between electrodes, thereby enabling extended operating temperature ranges without ESR penalty.
Solution Approach 2:
The patent employs porous carbonaceous materials with high surface area and developed pore structures (activated carbon, carbon nanotubes, graphite) that facilitate efficient ion access and transport. The porous structure increases the effective surface area for charge storage while maintaining low resistance pathways for ion movement, thereby reducing ESR and enabling stable operation at elevated temperatures.
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 ultracapacitor exhibits capacitance values of 6 Farads per cubic centimeter or more and low ESR at high temperatures, remaining stable for extended periods under various conditions, including high humidity and applied voltage.
Implementation Method 1
a nonaqueous electrolyte in ionic contact with the first electrode and the second electrode. The nonaqueous electrolyte contains an ionic liquid that is dissolved in an nonaqueous solvent
Implementation Method 2
a first electrode that comprises a first current collector electrically coupled to a first carbonaceous coating including activated carbon and a second electrode that comprises a second current collector electrically coupled to a second carbonaceous coating including activated carbon. Due to the effective surface area of the particles and the small spacing between the electrodes, large capacitance values may be achieved.
Data Source
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AI summary
An ultracapacitor that is in contact with a hot atmosphere having a temperature of about 80C or more is provided. The ultracapacitor contains a first electrode, second electrode, separator, nonaqueous electrolyte, and housing is provided. The first electrode comprises a first current collector electrically coupled to a first carbonaceous coating and the second electrode comprises a second current collector electrically coupled to a second carbonaceous coating. The capacitor exhibits a capacitance value within the hot atmosphere of about 6 Farads per cubic centimeter or more as determined at a frequency of 120 Hz and without an applied voltage.