The use of binary mixtures of 1-butyl-1-methylpyrrolidinium bis{(trifluoromethyl)sulfonyl}imide and aliphatic nitrile solvents as electrolyte for supercapacitors

Christoph Schütter,Alex R Neale,Patrick Wilde,Peter Goodrich,Christopher Hardacre,Stefano Passerini,Johan Jacquemin,Andrea Balducci

doi:10.1016/j.electacta.2016.10.088

Abstract

The development of high voltage electrolytes is one of the key aspects for increasing both energy and power density of electrochemical double layer capacitors (EDLCs). The usage of blends of ionic liquids and organic solvents has been considered as a feasible strategy since these electrolytes combine high usable voltages and good transport properties at the same time. In this work, the ionic liquid 1-butyl-1-methylpyrrolidinium bis{(trifluoromethyl)sulfonyl}imide ([Pyrr14][TFSI]) was mixed with two nitrile-based organic solvents, namely butyronitrile and adiponitrile, and the resulting blends were investigated regarding their usage in electrochemical double layer capacitors. Both blends have a high electrochemical stability, which was confirmed by prolonged float tests at 3.2V, as well as, good transport properties. In fact, the butyronitrile blend reaches a conductivity of 17.14mS·cm−1 and a viscosity of 2.46mPa·s at 20°C, which is better than the state-of-the-art electrolyte (1mol·dm−3 of tetraethylammonium tetrafluoroborate in propylene carbonate).

Highlights

In the field of electrochemical storage devices electrochemical double layer capacitors (EDLCs), which are known as supercapacitors, are typically the desired technology when confronted with applications where fast delivery and/or uptake of energy is needed [1,2,3,4]
In this manuscript we have reported about the use of blends of nitriles, namely BTN and ADN, and [Pyrr14][TFSI] in EDLCs
Investigations included the determination of physical and electrochemical properties

Summary

Introduction

In the field of electrochemical storage devices electrochemical double layer capacitors (EDLCs), which are known as supercapacitors, are typically the desired technology when confronted with applications where fast delivery and/or uptake of energy is needed [1,2,3,4]. In EDLCs, the high electrochemical stability of ILs translates into a maximum usable voltage for the final device as high as 3.2 V–3.5 V, affording an increase in energy density when compared to organic solvent based electrolytes [13]. Researching the processes taking place at the electrode-IL-interface appears to be a crucial step for tackling this issue [35,36,37,38] Another approach to overcome the issues of low transport properties of neat ILs is the use of blends with organic solvents. Starting with the evaluation of the transport properties (conductivity and viscosity), all important aspects for their implementation as EDLC electrolyte are investigated, including the electrochemical stability window, the maximum operative voltage, as well as, full cell tests to test their electrochemical stability in both short and long term measurements

Experimental

Results and discussion

Conclusion