Stable solvates in solution of lithium bis(trifluoromethylsulfone)imide in glymes and other aprotic solvents: Phase diagrams, crystallography and Raman spectroscopyElectronic supplementary information (ESI) available: Crystallographic data (single crystal data) in cif format (CCDC reference number 184345). See http://www.rsc.org/suppdata/cp/b2/b203776a/

Abstract

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.

Redox Active Glyme-Li Salt Solvate Ionic Liquids Based on Tetrabromoferrate(III)

“…Raman bands in the range of 800-900 cm ¹1 are assigned to a mixture of modes for CH 2 rocking vibrations and C-O-C stretching vibrations of glymes, and are thus useful to study the coordination structure of the complex cations. 38 For [Li(G3)][TFSA], a strong band emerged at around 870 cm ¹1 (the so-called breathing mode) along with weaker bands in the range of 800-850 cm…”

Review—Superconcentrated Electrolytes for Lithium Batteries

“…Otherwise, crystallization (deposition) of a Li salt or a Li salt solvate occurs upon increasing concentration, and the mixture is no longer a homogeneous electrolyte solution. Detailed phase diagrams of various Li salt-solvent mixtures obtained by Brouillette et al 32 and Henderson et al 40,41,[70][71][72][73] provide a useful guideline in selecting appropriate solvent and Li salt for highly concentrated electrolytes.…”

“…32,40,41,[70][71][72][73][74] The thermodynamic stability (thus a melting point) of these Li salt solvates should primarily be considered for designing highly concentrated electrolytes.…”

“…[24][25][26][27] Meanwhile, highly concentrated Li salt-glyme mixtures emerged as a new family of ionic liquids. At an early stage from the late 1990's to 2000's, they were studied as an amorphous analogue of Li + -conducting solid polymer electrolytes based on poly(ethylene oxide) (PEO), [28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] whose phase behavior and solvate structures were scrutinized by Henderson et al [33][34][35][36][37][38][39][40][41][42] From 2010 onward, Watanabe and his co-workers successively reported various physicochemical features analogous to ionic liquids in specific Li salt-glyme equimolar complexes, and established a new class of ionic liquids named "solvate ionic liquids" with clear classification criteria. 60 This review summarizes research activities on highly concentrated electrolytes for Li-based batteries.…”

Poly[bis(acetonitrile-κN)bis[μ3-bis(trifluoromethanesulfonyl)imido-κ4O,O′:O′′:O′′′]dilithium]

“…For a related structure of LiN(SO 2 CF 3 ) 2 , see: Henderson et al (2005); Davidson et al (2003); Brouillette et al (2002); Dillon et al (2001). For the structure of CH 3 CN with lithium salts, see: Klapö tke et al (2006); Brooks et al (2002); Yokota et al (1999); Raston et al (1989).…”