A new family of molten salts is reported, based on the N-alkyl, N-alkyl pyrrolidinium cation and the bis-(trifluoromethane sulfonyl)imide anion. Some of the members of the family are molten at room temperature, while the smaller and more symmetrical members have melting points around 100°C. Of the room-temperature molten salt examples, the methyl butyl derivative exhibits the highest conductivity; at 2 × 10 -3 S/cm this is the highest molten salt conductivity observed to date at room temperature among the ammonium salts. This highly conductive behavior is rationalized in terms of the role of cation planarity. The salts also exhibit multiple crystalline phase behavior below their melting points and exhibit significant conductivity in at least their higher temperature crystal phase. For example, the methyl propyl derivative (mp ) 12°C) shows ion conductivity of 1 × 10 -6 S/cm at 0°C in its higher temperature crystalline phase.

Many ionic liquids offer a range of properties that make them attractive to the field of electrochemistry; indeed it was electrochemical research and applications that ushered in the modern era of interest in ionic liquids. In parallel with this, a variety of electrochemical devices including solar cells, high energy density batteries, fuel cells, and supercapacitors have become of intense interest as part of various proposed solutions to improve sustainability of energy supply in our societies. Much of our work over the last ten years has been motivated by such applications. Here we summarize the role of ionic liquids in these devices and the insights that the research provides for the broader field of interest of these fascinating liquids.

The properties of a family of novel quaternary ammonium salts based on the bis(trifluoromethylsulfonyl)-imide and triflate anions are reported. Binary phase diagrams for some of their mixtures and their electrochemical windows of stability are also reported. The highest conductivity observed in the pure salt systems at 25°C was 7 × 10 -4 S cm -1 . An electrochemical window of stability of up to 5 V was measured on graphite electrodes. The effect of salt structure and solvent on conductivity of the salts is also discussed.

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