LiMn2O4 was examined as a cathode material for lithium-ion batteries, working together with a room temperature ionic liquid electrolyte, obtained by dissolution of solid lithium bis(trifluoromethanesulfonyl)imide (LiNTf2) in liquid N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide (MePrPipNTf2), with the formation of a liquid LiNTf2–MePrPipNTf2 system. The Li/LiMn2O4 cell was tested by galvanostatic charging/discharging and by impedance spectroscopy. The LiMn2O4 cathode showed good cyclability and Coulombic efficiency in the presence of 10wt.% of vinylene carbonate (VC) as an additive to the ionic liquid. The flash point of the LiNTf2–MePrPipNTf2–VC(10%) electrolyte was estimated to be above 300°C.