Transport and Electrochemical Properties and Spectral Features of Non-Aqueous Electrolytes Containing LiFSI in Linear Carbonate Solvents

Lithium bis(fluorosulfonyl)imide (LiFSI) has been investigated as a conducting salt of liquid electrolytes for lithium-ion batteries. It shows high solubility in most polar solvents, and a concentration of 5 M (mol dm(-3)) is reached in dimethyl carbonate (DMC) despite its low dielectric constant. LiFSI shows a thermal stability up to 180 degrees C on the thermogravimetric test. Compared with the LiPF6/carbonate electrolytes, the LiFSI-based ones show higher ionic conductivities over a wide temperature range (-50 to 50 degrees C) and higher lithium-ion transference numbers (t(Li+)) of 0.5-0.6. The conductivities of the LiFSI/DMC electrolyte over the 0.1-5 M concentration range obey a modified Casteel-Amis equation. The temperature dependence of 1 M LiFSI/DMC/EMC (3:7, v/v) is governed by the Vogel-Tammann-Fulcher relationship. The Fourier transform infrared spectra of the LiFSI/DMC electrolytes at different concentrations are systematically investigated. DMC shows significant spectral variations upon adding LiFSI, indicating strong interaction of Li+ cations with the solvent molecules. We also found that the compatibility with graphite anode and LiFePO4 cathode in the LiFSI-based electrolyte is as good as that in the LiPF6-based one, though aluminum (Al) corrosion occurs above 4 V vs Li+/Li. LiFSI is a very good contender to replace the latter, with increased performances and safety. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3514705] All rights reserved.