Lithium bis(trifluoromethylsulfone)imide (LiTFSI), a promising electrolyte for high energy lithium batteries, forms several stable solvates having low melting points in aprotic solvents. In a previous study (D. Brouillette, G. Perron and J. E. Desnoyers, J. Solution Chem., 1998, 27, 151), it was suggested, based on thermodynamic studies, that such stable solvates may persist in solution and influence their properties. To verify this hypothesis, phase diagrams and Raman spectra have been measured for solutions of LiTFSI in acetonitrile, propylene carbonate and glymes (n(ethyleneglycol) dimethyl ether or Gn), which have the chemical structure CH 3 -O-(CH 2 -CH 2 -O) n -CH 3 for n ¼ 1 to 4 and 10. The relative intensities of the LiTFSI and solvent Raman bands are proportional to the concentration for systems without solvates. The systems for which stable solvates were identified in the phase diagram show important changes in the relative intensities for both the LiTFSI and the solvent Raman bands at concentrations corresponding to particular stoichiometries and support the conclusion that stable solvates are present in the solutions. The structure of the crystalline G1:LiTFSI solvate was determined by X-ray crystallography. Structures for (G2) 2 :LiTFSI and (G1) 3 :LiTFSI solvates are proposed.

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In view of the high reactivity of the lithium metal, lithium batteries must operate in an aprotic environment, which can either be a conducting polymer; a liquid solvent, or a mixture of them. Two families of aprotic liquids were considered as solvents for lithium bis(trifluoromethylsulfone)imide (LiCF3SO2NSO2CF3 or LiTFSI). The first one is the substituted sulfamides, R1R2NSO2NR3R4, where the R groups are either methyl, ethyl, or methoxyethyl (CH,CHOOCH,), and the second one is the glymes, CH3O(CH2CH3O)CH3, for n up to 10. The phase diagrams, potential windows, conductivities, and the lithium interfacial resistances of the solutions were investigated, often as a function of temperature. The potential use of these solvents for different types of batteries is discussed.* Electrochemical Society Active Member. * * Electrochemical Society Student Member.making the molecule unsymmetrical and more polar, i.e., by replacing the ethyl groups by methyl or methoxyethyl groups, i.e., CH3CH2OCH3. The present paper deals with the phase diagrams, conductivities, potential windows, and lithium interfacial resistances of LiTFSI in these substituted sulfamides. The synthesis and properties of these liquid sulfamides is described elsewhere.'6 The use of these sulfamides as diluents for a polymer electrolyte is reported elsewhere.'7 The sulfamides used in this investigation are summarized in Table I where a short abbreviation is given for each.Another family of aprotic liquids which has proven interesting as solvents for high-energy batteries is the glymes18 or (polyethyleneglycol) dimethylether, CH,O(CH2CH,O)CH3.Unfortunately, the first member of the series, also called Sulfamtdes Rl\ '1? 1R,