Li-doped mixtures of alkoxy-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)-imide and organic carbonates as safe liquid electrolytes for lithium batteries

Abstract

The availability of safer electrolytes is an important target in the development of the new lithium batteries. The use of Li-doped mixtures based on ionic liquids and organic carbonates seems to be a very promising approach, because it allows to balance the non-flammability, high conductivity, low viscosity and good electrochemical stability.Here, we reported on the characterization of electrolytes solutions based on N-methoxyethyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)-imide (PYR1,2O1TFSI), EC/DEC binary system and LiTFSI, as potential safe electrolytes for lithium batteries. The mixtures were studied in terms of flammability tests, thermal features, physical properties, namely conductivity and viscosity, and electrochemical performances. We also carried out a comparison with the pure IL–Li salt system as well as with the standard electrolyte 1.0 M LiPF6 EC–DEC.The best solution showed ionic conductivity exceeding 7 mS cm−1 at 20 °C, room temperature viscosity lower of about 25 cPs and an overall electrochemical window of 4.5 V. With respect to the pure LiTFSI–IL electrolyte, a very stable interface with Li anode was also observed in at least for 20 storage days. This mixture was tested in a LiFePO4-based cell, and showed good performances at 1 C, assuring electrochemical stability for about 250 cycles with ∼100% efficiency.