Rechargeable LiFePO4 Cells Using N-Methyl-N-butyl pyrrolidinium bis(trifluoromethane sulfonyl)imide-LiTFSI Electrolyte Incorporating Polymer Additives

Rechargeable LiFePO4 Cells Using N-Methyl-N-butyl pyrrolidinium bis(trifluoromethane sulfonyl)imide-LiTFSI Electrolyte Incorporating Polymer Additives

TitleRechargeable LiFePO4 Cells Using N-Methyl-N-butyl pyrrolidinium bis(trifluoromethane sulfonyl)imide-LiTFSI Electrolyte Incorporating Polymer Additives
Publication TypeJournal Article
Year of Publication2008
AuthorsJoon Ho Shin, Pratyay Basak, John B Kerr, Elton J Cairns
JournalElectrochimica Acta
Volume54
Issue2
Pagination410-414
Date Published12/2008
KeywordsIonic liquid, lifepo4, lithium batteries, Lithium electrode, PEGDME, pyrrolidinium, TEGDME
Abstract

We have incorporated polymer additives such as poly(ethylene glycol) dimethyl ether (PEGDME) and tetra(ethylene glycol) dimethyl ether (TEGDME) into N-methyl-N-butylpyrrolidinium bis(trifluoromethane sulfonyl)imide (PYR14TFSI)-LiTFSI mixtures. The resulting PYR14TFSI + LiTFSI + polymer additive ternary electrolyte exhibited relatively high ionic conductivity as well as remarkably low viscosity over a wide temperature range compared to the PYR14TFSI + LiTFSI binary electrolytes. The charge/discharge cyclability of Li/LiFePO4 cells containing the ternary electrolytes was investigated. We found that Li/PYR14TFSI + LiTFSI + PEGDME (or TEGDME)/LiFePO4 cells containing the two different polymer additives showed very similar discharge capacity behavior, with very stable cyclability at room temperature (RT). Li/PYR14TFSI + LiTFSI + TEGDME/LiFePO4 cells can deliver about 127 mAh/g of LiFePO4 (74.7% of theoretical capacity) at 0.054 mA/cm2 (0.2C rate) at RT and about 108 mAh/g of LiFePO4 (63.4% of theoretical capacity) at 0.023 mA/cm2 (0.1C rate) at −1 °C for the first discharge. The cell exhibited a capacity fading rate of approximately 0.09-0.15% per cycle over 50 cycles at RT. Consequently, the PYR14TFSI + LiTFSI + polymer additive ternary mixture is a promising electrolyte for cells using lithium metal electrodes such as the Li/LiFePO4 cell reported here. These cells showed the capability of operating over a significant temperature range (~0-~30 °C).

DOI10.1016/j.electacta.2008.07.062