Ion Storage in Nanoconfined Interstices Between Vertically Aligned Nanotubes in Electric Double-Layer Capacitors

Abstract

Ionic liquids are considered promising electrolytes for developing electric double-layer capacitors (EDLCs) with high energy density. To identify optimal operating conditions, we performed molecular dynamics simulations of N-methyl-N-propyl pyrrolidinium bis(trifluoromethanesulfonyl)imide (mppy+ TFSI−) ionic liquid confined in the interstices of vertically aligned carbon nanostructures mimicking the electrode structure. We modeled various surface charge densities as well as varied the distance between nanotubes in the array. Our results indicate that high-density ion storage occurs within the noninteracting double-layer region formed in the nanoconfined domain between charged nanotubes. We determined the specific arrangement of these ions relative to the nanotube surface and related the layered configuration to the molecular structure of the ions. The pitch distance of the nanotube array that enables optimal mppy+ TFSI− storage and enhanced capacitance is determined to be 16 Å.

Design of Supercapacitor Electrodes Using Molecular Dynamics Simulations

“…The obtained curve of capacitance versus diameter is consistent with the experimental results [ 11 ]. For the CNT forest, the simulation work of Dive and Banerjee indicated the highest efficiency of charge storage for the interval spacing of 1.6 nm, compared to those of 1.2 and 2.0 nm [ 128 ].…”

A Comparative Study of Imidazolium-Based Ionic Liquid-Single-Walled Carbon Nanotube Composites with Enhanced Conductivity Properties for Supercapacitor Applications

“…Due to growing global environmental concerns, there are increasing demands for environmentally-friendly, efficient, renewable energy storage devices (1)(2)(3). Batteries, fuel cells, and supercapacitors are useful energy storage devices that function on the principle of electrochemical energy conversion (1).…”

“…Batteries, fuel cells, and supercapacitors are useful energy storage devices that function on the principle of electrochemical energy conversion (1). Supercapacitors have many improved properties over batteries and fuel cells, which include higher power density, shorter charge time, and longer life cycles, and thus they have various potential applications (1)(2)(3)(4)(5). Supercapacitors can be used as power supplies in small portable devices, and they can be used to provide energy in rural areas where costly electrical infrastructures are not available.…”

“…For optimal operation, supercapacitors require electrodes with high surface area, high conductivity, and suitable temperature and chemical stability (1,3,7). Carbon-based nanomaterials have been considered as promising electrodes for supercapacitors due to their unique high surface area, high conductivity and stability properties, and low cost (1,4,8,9).…”