Phosphonium ILs have been less explored compared to their ammonium analogues, even though they offer the advantages of lower cost, lower viscosity, higher conductivity, better thermal stability, and wider electrochemical windows. Cyclic phosphonium ILs are thus far unreported. Recent reports on the physical properties of piperidinium and azepanium suggest that the analogous cyclic phosphonium compounds are expected to exhibit superior physical properties for battery applications. Cyclic phosphonium bis(trifluoromethylsulfonyl)imide (NTf2) ILs bearing alkyl or phenyl substituents were synthesized, and their structures were confirmed using 1H, 13C and 31P Nuclear Magnetic Resonance spectroscopy. We report here on the conductivity, viscosity, self diffusion coefficients and thermal properties of the phospholanium and phosphinanium salts. The cyclic phosphonium salts appear to exhibit higher viscosities than their ammonium analogues and higher thermal decomposition temperatures.  This work was supported in part at BNL by the DOE Office of Basic Energy Sciences, under contract # DE-AC02-98CH10886.

Cyclic phosphonium ionic liquids

244th National Meeting (2012)

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