Comparing the performance of sulfonium and phosphonium ionic liquids as electrolytes for supercapacitors by molecular dynamics simulations

AM Sampaio and GFL Pereira and M Salanne and LJA Siqueira, ELECTROCHIMICA ACTA, 364, 137181 (2020).

DOI: 10.1016/j.electacta.2020.137181

Ionic liquids (ILs) are generally considered good candidates for supercapacitors electrolytes due to their wide electrochemical windows (EW), which results in high energy densities. Yet they generally offer poor power delivery compared to the conventional organic electrolytes. Here we performed molecular dynamics simulations of slit porous electrode in contact with two ionic liquids with similar viscosities and ionic conductivities, but different electrochemical stability. They are formed by sulfonium and phosphonium cations sharing the same anion. The supercapacitor built with sulfonium-based IL can store up to 50 % more energy at high voltage (Delta Psi = 3.8 V) than the one involving the phosphonium-based IL. Contrarily to previous works with ILs, the improved performance in terms of energy density is accompanied with a faster charging. The properties are rationalized by comparing the structure of the liquids in the two systems. These results show that it is not always necessary to compromise the power delivery for enhanced energy density in ionic liquids-based supercapacitors. (C) 2020 Elsevier Ltd. All rights reserved.

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