Room-temperature ionic liquids (RTILs) have emerged as a very promising class of electrolytes used in supercapacitors, due to their exceptionally wide electrochemical stability window, excellent thermal stability, non-volatility and relatively inert nature. In spite of a remarkable increase in the number of RTILs reported, a majority of RTILs under investigation are monocationic ionic liquids (MILs) that have monovalent cations. In contrast to MILs, dicationic ionic liquids (DILs), with each dication carrying two positive unit charges, can achieve higher thermal stability. However, to date very few efforts have been devoted into exploration of DILs, especially, when used as electrolytes in supercapacitors.We performed molecular dynamics (MD) simulations to study the bulk properties of DILs 1-alkyl-3-dimethylimidazolium tetrafluoroborate. The influences of the linkage chain length on the nanoscale organization of DILs were explored in comparison with those of MILs with varying free alkyl chain length. To study the effect of anion type on the nanoscale ordering of ILs, hexafluorophosphate and bromine anions were used to replace tetrafluoroborate ions for short- and long-chain dications and monocations. Taking DILs as electrolytes in supercapacitors with carbon electrodes, we investigated the interfacial structure and electrochemical performance of DILs with different linkage chains, using MD simulation for comparison with their monocationic counterparts. We found that DILs yielded higher differential capacitance in contrast to MILs with certain anions, which was substantiated by cyclic voltammetry (CV) measurements.

Dicationic ionic liquids in bulk and at carbon surfaces

247th National Meeting (2014)

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