Preparation of imidazolium based polymerized ionic liquids gel polymer electrolytes for high-performance lithium batteries

Abstract

Ionic liquid gel polymer electrolytes (GPE) possess advantages of high ionic conductivity, outstanding safety and high compatibility with electrodes. However, the ionic liquid plasticizers in GPE for elevating the ionic conductivity will decrease the mechanical strength of GPE. Polymerized ionic liquids (PIL) combine the properties of polymer and ionic liquids, so the application of them possesses several superiorities beyond ionic liquids. In this research, one PIL poly(1-[2-(2-(2-(Methacryloyloxy)ethoxy)ethoxy)ethyl]-3-methylimidazolium bis(trifluoromethylsulfonyl)imide)-co-poly(poly(ethylene glycol) methyl ether methacrylate) is synthesized and blended with host polymer PVDF, ionic liquid (1-butyl-1-methylimidazolium bis(trifluoromethylsulfonyl)imide, [BMIM]TFSI) and lithium salt LiTFSI to prepare PIL gel electrolyte (PIL-GPE@IL) membrane applying in lithium battery. Besides the moderate mechanical strength, the PIL-GPE@IL combined with ionic liquid display a high ion conductivity of 1.76 × 10−3 S cm−1 at 30 °C and outstanding electrochemical stability with an oxidation potential of 4.26 V vs. Li+/Li. Furthermore, the Li/LiFePO4 cells assembled with the PIL-GPE@IL show excellent rate performance and cycle performance, which exhibit an initial specific discharge capacity of approximate 143 mAh g−1 at current density of 0.5C accompanied by an excellent capacity retention of 97% within 120 cycles. This work demonstrates the capability of the as-prepared PIL-GPE@IL using in lithium batteries to boost the performance.