The enormous demands on available global lithium resources have raised concerns about the sustainability of the supply of lithium. Sodium secondary batteries have emerged as promising alternatives to lithium batteries. We describe here sodium bis(trifluoromethylsulfonyl) amide (NaNTf2) electrolyte systems based on 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl) amide (C(4)mpyrNTf(2)) ionic liquids. The electrochemical stability of the system was examined; a pair of facile cathodic and anodic processes around 0 V vs. Na/Na+ were observed in cyclic voltammetry measurements and interpreted as deposition and dissolution of sodium metal. Density, viscosity and conductivity of the electrolytes were studied. It was found that the ionic conductivity of electrolytes reached as high as 8 mS/cm, decreasing slowly as the salt content increased due to increasing of viscosity and density of the electrolyte. Therefore, sodium electrolytes based on C(4)mpyrNTf(2) appear to be promising for secondary sodium battery applications. (C) 2013 Elsevier Ltd. All rights reserved.