Ether-functionalized pyrazolium ionic liquids as new electrolytes for lithium battery

Two new functionalized ILs based on pyrazolium cations and bis(trifluoromethylsulfonyl)imide anions (TFSI−) were synthesized and characterized. Their physicochemical and electrochemical properties, including melting point, thermal stability, density, viscosity, conductivity, and electrochemical window were investigated. The two ILs had low melting points and wide electrochemical windows. Behaviors of lithium redox, chemical stability against lithium metal, and charge–discharge cycle performance of lithium battery were also examined for the two IL electrolytes with 0.4 mol kg−1 LiTFSI. The IL electrolytes showed good chemical stability against lithium metal, and Li/LiFeO4 cells using the two IL electrolytes without additives owned good capacity and cycle property at the current rate of 0.1 C.

► New ether-functionalized pyrazolium ILs are reported.
► They have low melting point and good electrochemical stability.
► Li/LiFePO4 cells using the IL electrolytes have good capacity and cycle property.