Comparison of the thermodynamic and transport properties of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) with LiClO4 and Bu4NBr in water at 25°C

Lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) is a promising electrolyte for lithium batteries. While it presents many interesting features in aprotic solvents (high solubility and conductivity, electrochemical stability, etc.), little is known about its properties in water. The solid-liquid phase diagram, surface tension, volume, heat capacity, and conductivity were therefore measured at 25 degrees C and compared with the same properties of typical hydrophilic (LiClO4) and hydrophobic (Bu4NBr) electrolytes. To help in the comparison, some of the literature data for LiClO4 and Bu4NBr were extended. The standard Lambda(0), V-2(0), and C-P,2(0), are respectively 71.12 S cm(2) mol(-1), 139.7 cm(3) mol(-1), and 543 J K-1 mol(-1) at 25 degrees C. LiTFSI is quite soluble, and shows surface activity and a small tendency for self-association in water. The aggregation number estimated from a mass-action model is of the order of 4.