Characterization of N-methyl-N-butylpyrrolidinium Bis(trifluoromethanesulfonyl)imide-LiTFSI-Tetra(ethylene glycol) dimethyl ether mixtures as a li metal cell electrolyte

We have employed tetra(ethylene glycol)dimethyl ether (TEGDME) as a polymer solvent in mixed electrolytes composed of N-methyl-n-butyl pyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI), LiTFSI, and TEGDME and characterized their physical and electrochemical properties as well as the cyclability of Li/S cells with PYR14TFSI+x LiTFSI (x=moles LiTFSI/kg PYR14TFSI)+y TEGDME (y=kg TEGDME/kg PYR14TFSI) electrolyte. The addition of the TEGDME polymer solvent to the PYR14TFSI+0.2 m LiTFSI+y TEGDME mixtures resulted in a significant enhancement of ionic conductivity, particularly at lower temperatures. Interfacial impedance and galvanostatic Li cycling measurements show that the PYR14TFSI+0.2 m LiTFSI+y TEGDME ternary mixture exhibits excellent compatibility with Li metal electrodes. The use of the ternary mixture as an electrolyte in a Li/S cell provided good charge and discharge capability of the cell at room temperature with a discharge capacity of 887 mAh/g sulfur at 0.054 mA/cm(2) and at low temperature (similar to 0 degrees C) with a discharge capacity of about 440 mAh/g sulfur at 0.033 mA/cm(2) for the first cycle, respectively (theoretical specific capacity 1672 mAh/g sulfur). In addition, the cell tested at 0 degrees C exhibited a stable cyclability after the 5th cycle, with a discharge capacity of 248 mAh/g sulfur for the 20th cycle. (c) 2008 The Electrochemical Society.