7Li and 19F diffusion coefficients and thermal properties of non-aqueous electrolyte solutions for rechargeable lithium batteries

In this paper, electrolyte solutions of ethylene carbonate (EC) and ethylene methylene carbonate (EMC) with different salts as LiPF6, LiBF4 and LiN(SO2C2F5)(2) were prepared and characterized using Pulsed Field Gradient (PFG) NMR and DSC. Cation transport numbers, tau(+), ranging between 0.37 and 0.49 were obtained, The maximum value of 0.49 was obtained in the case of a 0.5 M solution of LiBF4 in 2:8 EC:EMC. The DSC data suggest that the increase of EMC stabilizes the electrolyte solution towards low temperature, and that a 2:8 EC:EMC ratio assures good stability at low temperature to the electrolyte solution. While LiN(SO2C2F5)(2) seems to score the best in terms of low temperature stability, LiPF6 may offer the best cost/performances compromise. (C) 1999 Elsevier Science S.A. All rights reserved.