Gelled ionic liquid sodium ion conductors for sodium batteries

Owing to the unique properties of certain Ionic liquids (ILs) as safe and green solvents, as well as the potential of sodium as an alternative to lithium as charge carriers, we investigate gel sodium electrolytes as safe, low cost and high performance materials with sufficient mechanical properties for application in sodium battery technologies. We investigate the effect of formation of two types of gel electrolytes on the properties of IL electrolytes known to support Na/Na+ electrochemistry. The ionic conductivity is only slightly decreased by 0.0005 and 0.0002 S cm(-1) in the case of 0.3 and 0.5 M NaNTf2 systems respectively as the physical properties transition from liquid to gel. We observed facile plating and stripping of Na metal around 0 V vs. Na/Na+ through the cyclic voltammetry. A wide-temperature range of the gelled IL state, of more than 100 K around room temperature, is achieved in the case of 0.3 and 0.5 M NaNTf2. We conclude that the formation of a gel does not significantly affect the liquid-like ion dynamics in these materials, as further evidenced by DSC and FTIR analysis. (C) 2015 Elsevier Ltd. All rights reserved.