Asymmetrical Supercapacitor Based on Iodide Ion Containing Ionic Liquid Mixture
Authors: Thomberg Thomas , Janes Alar , Lust Enn 
Published: December 2024

The increased global energy demand and environmental pollution require energy generated from renewable energy sources such as wind, solar, etc. As the adoption of these energy resources increases, developing different energy storage systems becomes important. The applicability of room-temperature ionic liquids (RTILs) as electrolytes for supercapacitors (SCs) and batteries has been discussed in many papers. RTILs have lower conductivity and higher viscosity; thus, they have narrower low-temperature operation limits compared to aqueous and non-aqueous electrolytes. However, compared with volatile aqueous and organic electrolytes, RTILs are much safer in SCs applications. To improve the power and energy densities of SCs, various mixtures of ionic liquids have been investigated, including systems of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4) with bromide ion addition on carbon cloth1, EMImBF4 with iodide ion addition on Bi(111) electrode2 and D-glucose derived activated carbon (GDAC)3. However, in studies1,3 the capacitance and ideal polarizability of positively and negatively charged carbon cloth and GDAC electrodes were not taken into account, limiting the overall energy storage capability, efficiency, and cycle life of these systems. Therefore, characterization of these materials-based SCs in three- and two-electrode configurations are inevitable to overcome these mentioned shortcomings4. In the present research EMImBF4 with addition of 5 wt% 1-ethyl-3-methylimidazolium iodide (EMImI) was selected to study the influence of iodide anions addition on the electrochemical performance of micro- and mesoporous carbon material-based SC system4. Based on electrochemical data established by cyclic voltammetry, electrochemical impedance spectroscopy, constant current charge/discharge, and constant power discharge methods, the asymmetrical SC with ionic liquid mixture compared to the symmetrical SC with neat EMImBF4 demonstrated increase in cell capacitance about 5 F g-1 (33 F g-1 vs 27 F g-1 in cell potential range of 2.4 V) and specific energy about 3.5 W h kg-1 (28.1 W h kg-1 vs 24.4 W h kg-1 in cell potential range of 2.4 V). However, the ideal polarizability region, i.e., electrochemical stability of the iodide ion containing ionic liquid mixture-based SC is somewhat lower as well as specific adsorption and partial charge transfer is not fully reversible leading to the lower coulombic and energy efficiency values4.

Acknowledgments:

This research was supported by the EU through the European Regional Development Fund under project TK141, "Advanced materials and high-technology devices for energy recuperation systems" (2014–2020.4.01.15–0011) and TK210, “Estonian Centre of Excellence in Green Hydrogen and Sustainable Energetics”, Institutional Research grant IUT20–13, European Spallation Source: Estonian Partition in ESS Instrument design, development and building and application for science research project SLOKT12026T and by Estonian Research Council grants PUT1033, PUT55, and PRG676.

References:

1S. Yamazaki, T. Ito, M. Yamagata, M. Ishikawa, Electrochim. Acta, 2012, 86, 294-297.

2L. Siinor, C. Siimenson, K. Lust and E. Lust, Electrochem. Commun, 2013, 35, 5-7.

3T. Thomberg, T. Tooming, L. Siinor, K. Tõnurist, A. Jänes, E. Lust, J. Electrochem. Soc., 2014, 160(3), A222-227.

4T. Thomberg, E. Lust, A. Jänes, J. Energy. Storage, 2020, 32, 101845.