CNT Ultracapacitor Electrodes for High-Frequency Capacitive Response
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Solution Overview
Problem
Conventional ultracapacitors perform poorly at high frequencies, making them unsuitable for applications such as power factor correction devices due to significant deviations from ideal capacitor behavior.
Innovation Solution
Development of electric double-layer capacitors (EDLCs) with carbon nanotubes directly formed on current collectors and an electrolyte in between, configured to maintain capacitive performance up to 50 Hz with reduced equivalent series resistance (ESR) and leakage resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional ultracapacitor structures are used, then manufacturing is simpler, but high frequency performance deteriorates with significant deviation from ideal capacitor behavior
Solution Approach 1:
The patent changes the physical and chemical parameters of the electrode materials by using carbon nanotubes with specific structural characteristics (length, diameter, alignment) and treating them with acids to modify surface properties. These parameter changes enable the ultracapacitor to maintain ideal capacitor behavior at high frequencies up to 100 Hz while preserving the basic device structure
Solution Approach 2:
The patent employs composite electrode structures combining carbon nanotubes with conductive polymers or metal oxides. This composite approach enhances the high frequency response and reduces equivalent series resistance while maintaining structural simplicity, resolving the contradiction between performance improvement and device complexity
2Reliability
If carbon nanotubes are directly formed on current collectors, then high frequency response improves, but manufacturing complexity increases
Solution Approach 1:
The patent applies preliminary treatments to the current collector surface before carbon nanotube formation, including surface roughening, oxidation, or deposition of catalyst layers. These preliminary actions facilitate subsequent CNT growth directly on the current collector, achieving high frequency performance while streamlining the manufacturing process
Solution Approach 2:
The patent utilizes self-organizing properties of carbon nanotubes during chemical vapor deposition or other growth processes. The nanotubes automatically align and form uniform structures on the current collector without requiring complex external guidance systems, improving manufacturability while maintaining the direct formation approach for high frequency response
3Reliability
If EDLC structure with directly formed CNTs is used, then equivalent series resistance decreases, but manufacturing precision requirements increase
Solution Approach 1:
The patent optimizes parameters such as CNT length (1-10 micrometers), diameter (10-100 nanometers), and surface density to achieve low ESR. By controlling these parameters within specific ranges through adjusted deposition conditions and post-treatment processes, the patent reduces manufacturing precision requirements while maintaining effective ESR reduction
Solution Approach 2:
The patent employs porous electrode structures formed by carbon nanotube forests with controlled porosity and pore size distribution. This porous architecture provides multiple electrolyte access paths and increases effective surface area, reducing ESR through enhanced ion transport while tolerating broader manufacturing variations
4Power
If ultracapacitors are designed for high frequency operation, then power delivery improves, but energy storage capacity may be reduced
Solution Approach 1:
The patent implements local quality optimization by creating regions of high surface area carbon nanotubes near the current collector for rapid charge transfer and power delivery, while maintaining sufficient overall capacitance through extended electrode structures. This spatial differentiation enables simultaneous achievement of high power capability and adequate energy storage capacity
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 EDLCs demonstrate improved performance at high frequencies, maintaining capacitance and phase shift within desired ranges, enabling their use in high-frequency applications like power factor correction devices with reduced energy storage losses.
Implementation Method 1
a first electrode including a first current collector and first plurality of carbon nanotubes (CNTs) disposed (e.g., formed) substantially directly upon the first current collector
Implementation Method 2
an electrolyte disposed between and in contact with (e.g., wetting) the first and second electrodes
Data Source
AI summary
An electric double layer capacitor (EDLC) is disclosed including: a first electrode including a first current collector and first plurality of carbon nanotubes (CNTs) disposed substantially directly upon the first current collector; a second electrode comprising a second current collector and second plurality of CNTs disposed substantially directly upon the second current collector; and an electrolyte disposed between and in contact with (e.g., wetting) the first and second electrodes. In some embodiments, the EDLC is configured to have a capacitive frequency window comprising about 1 Hz to about 50 Hz.