Abstract
A series of hydrophobic room temperature ionic liquids (ILs) based on ethereal functionalised pyrrolidinium, piperidinium and azepanium cations bearing the bis[(trifluoromethyl)sulfonyl]imide, [TFSI]−, anion were synthesized and characterized. Their physicochemical properties such as density, viscosity and electrolytic conductivity, and thermal properties including phase transition behaviour and decomposition temperature have been measured. All of the ILs showed low melting point, low viscosity and good conductivity and the latter properties have been discussed in terms of the IL fragility, an important electrolyte feature of the transport properties of glass‐forming ILs. Furthermore, the studied [TFSI]−‐based ILs generally exhibit good electrochemical stabilities and, by coupling electrochemical experiments and DFT calculations, the effect of ether functionalisation at the IL cation on the electrochemical stability of the IL is discussed. Preliminary investigations into the Li‐redox chemistry at a Cu working electrode are also reported as a function of ether‐functionality within the pyrrolidinium‐based IL family. Overall, the results show that these ionic liquids are suitable for electrochemical devices such as battery systems, fuel cells or supercapacitors.
Highlights
Ionic liquids have gained considerable interest over the past few decades due to their numerous attractive properties such as extremely low vapour pressure, low flammability, high thermal stability and large liquid range
In order to develop ILs with good physiochemical properties for possible energy applications, we have investigated the effect of cation structural modifications for a family of ILs based on pyrrolidinium, piperidinium and azepanium cations functionalised with two or four ether groups paired with the benchmark [TFSI]À anion
Initial attempts to synthesise these materials using conventional alkylation procedures employed for imidazolium-based ILs proved problematic due to the low alkylation yield observed between the alkylamine and the ethereal precursors
Summary
Ionic liquids have gained considerable interest over the past few decades due to their numerous attractive properties such as extremely low vapour pressure, low flammability, high thermal stability and large liquid range This has led to a number of groups researching ionic liquid applications in the fields of catalysis[1,2,3], separation [4,5] and nanotechnology.[6] In comparison with molecular solvents, ionic liquids possess good ionic conductivity coupled with good electrochemical stability and, have been proposed as new electrolytes for energy devices[7,8,9,10,11,12,13,14,15,16,17,18] and as solvents for electrodeposition of metals.[19,20].
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