Two new functionalized ionic liquids (ILs) based on guanidinium cation with two ether groups and TFSA− anion are synthesized and characterized. Their physicochemical and electrochemical properties, including melting point, thermal stability, density, viscosity, conductivity, and electrochemical window are determined. Both the ILs are liquids at room temperature, and the viscosities are about 60mPas at 25°C. Behavior of lithium redox, chemical stability against lithium metal and charge–discharge characteristics of lithium battery, are also examined for the two ILs as electrolyte with 0.6molkg−1 LiTFSA. Though the cathodic limiting potentials of the two ILs are higher than 0V versus Li/Li+, the lithium plating and stripping on Ni electrode can be observed in the two IL electrolytes, indicating their good chemical stability against lithium metal. Li/LiFePO4 cells using the two IL electrolytes without any additive showed good cycle property at the current rate of 0.2C at 25°C and 55°C.