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

Abstract

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 °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 Λ0, [Formula: see text] and [Formula: see text] are respectively 71.12 S cm2 mol−1, 139.7 cm3 mol−1 and 543 J K−1 mol−1at 25 °C. LiTFSI s 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. Keywords: lithium bis(trifluoromethylsulfonyl)imide, lithium perchlorate, tetrabutylammonium bromide, volume, heat capacity, phase diagram, thermal analysis, surface tension, conductance.