Six low-viscosity ionic liquids based on trialkylimidazolium cation with one or two ether groups and TFSA− anion are used as new electrolytes for lithium battery, and compared with three typical trialkylimidazolium ILs without ether group. It is found that ether group in trialkylimidazolium cation can have an obvious effect on properties of electrolyte and performances of lithium battery. Introducing of ether group into trialkylimidazolium cation can be benefit for lithium redox behavior on Ni electrode, and affect passivation layer between IL electrolyte and lithium metal. Li/LiFePO4 cells using these ether-functionalized IL electrolytes without additive have good battery performance, and IM(2o1)1(2o2)-TFSA electrolyte owns better rate property.