Cross-linked polymeric ionic liquids ion gel electrolytes by in situ radical polymerization

Abstract

In this work, the free-standing ion gel polymer electrolytes (IGPEs) membranes have been successfully prepared by in situ polymerization of N-Vinyl-3-butyl imidazole bis(trifluoromethylsulfonyl)imide (VBImTFSI) and poly(ethylene glycol) methacrylate (PEGMA) in the presence of 1-butyl-3-methylimidazolium bis-(trifluoromethylsulfonyl)imide ([BMIM]TFSI) and a small amount of a cross-linker, with/without lithium salt. The obtained semitransparent and flexible IGPEs membranes exhibit good thermal stability and mechanical strength. The ionic conductivity is improved with increasing ionic liquid content and with the addition of lithium salt and the ionic conductivity is up to 2.11 × 10−4 S cm−1 at room temperature. The IGPEs containing LiTFSI exhibit wide electrochemical stability up to 4.9 V versus Li+/Li, and a superior lithium-ion transference number (tLi+) of 0.83. In addition, Li/LiFePO4 half cells assembled with the optimized IGPEs exhibit high charge/discharge efficiency and stable cycle performance at C/10 rate, delivering a discharge capacity of 142.2 mA h g−1 with stable coulombic efficiency (100%) after 100 cycles.