Relation between the ion size and pore size for an electric double-layer capacitor.

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Electrochemical double layer capacitors (EDLCs) bridge the performance gap between dielectric capacitors and batteries.
• Fundamental understanding of the relationship between carbon electrode pore size and electrolyte ion size for optimal capacitance remains incomplete.

Purpose of the Study:

• To determine the optimal pore size of TiC-derived carbon electrodes for maximum capacitance in EMI-TFSI ionic liquid.
• To investigate the impact of pore size deviation from ion size on capacitance.
• To propose a general strategy for designing EDLCs with enhanced energy density.

Main Methods:

• Fabrication of TiC-derived carbon electrodes at 500°C.
• Electrochemical characterization of capacitance in EMI-TFSI ionic liquid.
• Analysis of capacitance as a function of electrode pore size and electrolyte ion size.

Main Results:

• Maximum double-layer capacitance achieved when TiC-derived carbon electrode pore size closely matches the EMI-TFSI ion size (approx. 0.7 nm).
• Capacitance values exceeding 160 F/g and 85 F/cm³ were recorded for optimized TiC-CDC.
• Significant capacitance decrease observed with pore size deviations as small as one angstrom from the optimal value.

Conclusions:

• Sub-angstrom accuracy in tuning carbon electrode pore size relative to electrolyte ion size is critical for maximizing EDLC capacitance.
• The findings provide a generalizable approach for designing high-energy-density EDLCs.
• This strategy has been validated for both solvent-free and solvated electrolytes.