Abstract
Electrochemical capacitors (ECs) are electrical energy storage devices that have the potential to be very useful in a wide range of applications, especially where there is a large disparity between peak and average power demands. The use of ionic liquids (ILs) as electrolytes in ECs can increase the energy density of devices; however, the viscosity and conductivity of ILs adversely influence the power density of the device. We present experimental results where several ILs containing different cations have been employed as the electrolyte in cells containing mesoporous carbon electrodes. Specifically, the behavior of ILs containing an ether bond in an alkyl side chain are compared with those of a similar structure and size but containing purely alkyl side chains. Using electrochemical impedance spectroscopy and constant current cycling, we show that the presence of the ether bond can dramatically increase the specific capacitance and reduce device resistance. These results have the important implication that such ILs can be used to tailor the physical properties and electrochemical performance of IL-based electrolytes.
Highlights
Electrochemical capacitors (ECs), often referred to as supercapacitors, are electrical energy storage devices that absorb and release charge at relatively high rates when compared with electrochemical cells.[1]
Charge is stored through two different mechanisms in ECs; in electrical double-layer capacitors (EDLCs), energy is stored through the physical separation of charges at the electrode− electrolyte interface, whereas in pseudocapacitors, fast redox reactions result in the transfer of charge between the electrolyte and electrode.[1]
A conventional EDLC electrolyte is a solution of tetraethylammonium tetrafluoroborate (TEABF4) in acetonitrile and is limited to an operating potential of roughly 2.7 V
Summary
The viscosity of ILs has been found to have considerable influence over their performance as EC electrolytes[22] as it partly defines the conductivity of the IL. A further possibility is that the ether bond introduces a small electronegative region to the cation structure that facilitates a denser packing of ions at the electrode surface, thereby resulting in a greater amount of charge being displaced in the electrode These results show that despite ILs being more viscous and less conductive than conventional electrolytes, their physical properties can be manipulated through the inclusion of an ether bond into an alkyl side chain of the cation. This provides much scope for future research as the performance of ECs will be improved by the production of more conductive IL electrolytes alongside the development of electrode materials with suitable pore characteristics, tailored to the ILs in question. This material is available free of charge via the Internet at http://pubs.acs.org
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
