Four new functionalized ILs based on pyrazolium cations and bis(trifluoromethylsulfonyl)imide anions (TFSI−) are synthesized and characterized. These ILs show low-melting point and low-viscosity characteristics, and the viscosity of OEPZ–TFSI is 41.2 mPa s at 25 °C. These IL electrolytes with 0.4 mol kg−1 LiTFSI have good chemical stability against lithium metal. Li/LiFeO4 cells using these IL electrolytes without additives own good electrochemical performance, and the cells using OMPZ–TFSI and OEPZ–TFSI electrolytes own better rate property.