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 degrees 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. (C) 2012 Elsevier B.V. All rights reserved.