Electrochemical Characterization of Two Types of PEO-Based Polymer Electrolytes with Room-Temperature Ionic Liquids

Abstract

Two types of gel polymer electrolytes containing ionic liquids, 1-ethyl-3-methylimidazolium bis?trifluoromethanesulfonyl?imide ?EMI-TFSI? and N-methyl-N-propylpiperidinium bis?trifluoromethanesulfonyl?imide ?PP13-TFSI?, are prepared by the solution casting method. Fourier-transform infrared spectroscopy indicates that incorporating both EMI-TFSI and PP13-TFSI can change the phase structure of poly?ethylene oxide??PEO? and cause a more amorphous phase, can weaken the association between Li+ and TFSI−, and cause more free Li+. The TFSI− anion from these two kinds of ionic liquids plays a main plasticizing role in the P?EO?20LiTFSI systems. From cyclic voltammetry results, the good reversibility of the Li deposition and dissolution, as well as a stable interfacial passive film, can be expected by incorporating PP13-TFSI and a relatively small quantity of EMI-TFSI. The addition of EMI-TFSI and PP13-TFSI to P?EO?20LiTFSI polymer electrolyte results in an increase of the ionic conductivity, a wider electrochemical stability window, a decrease of the glass transition temperature ?Tg?, and a better interfacial stability. The tests performed on Li metal/LiFePO4 batteries containing these two types of polymer electrolytes have shown a good capacity performance at a moderate temperature.