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

In this paper, electrolyte solutions of ethylene carbonate (EC) and ethylen e methylene carbonate (EMC) with different salts as LiPF6, LiBF4 and LiN(SO 2C2F5)(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 increas e of EMC stabilizes the electrolyte solution towards low temperature, and t hat a 2:8 EC:EMC ratio assures good stability at low temperature to the ele ctrolyte solution. While LiN(SO2C2F5)(2) seems to score the best in terms o f low temperature stability, LiPF6 may offer the best cost/performances com promise. (C) 1999 Elsevier Science S.A. All rights reserved.