High conductivity of superionic-glass-in-ionic-liquid solutions

As a further example of the extraordinary solvent powers of ambient temperature molten salts (ATMS or "ionic liquids'') we demonstrate that lithium thiophosphate glasses, well known for their unicationic conduction mechanism, and high ambient conductivity, dissolve in the ATMS ethylmethylimidazolium tetrafluoroborate up to 30 mol %. Remarkably, the conductivity of this solution is higher than that of a solution of the same lithium salt content made with the salt lithium TFSI [bis(trifluoromethanesulfonyl)imide] which bestows high conductivity on most other solvents. The glass-saturated melt has almost the same conductivity as the glass itself. However their glass temperatures differ by some 200 K so it is clear that the solution retains little if any of the decoupled Li+ conduction mechanism of the glass. It may nevertheless make a suitable electrolyte for lithium cells of a novel kind. Since the ionic liquids may be incorporated in polymer gel electrolytes without significant loss of conductivity, the present solutions may prove valuable for solid-state electrochemical device applications. (C) 2003 The Electrochemical Society.