We evaluated the charge-discharge behavior of a LiNi 1/3 Mn 1/3 Co 1/3 O 2 (NMC) electrode in a 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMImFSI) ionic liquid. At 163 mAh g −1 after 50 cycles, the discharge capacity of the NMC cathode in LiTFSI/EMImFSI (TFSI − = bis(trifluoromethylsulfonyl)imide) at 1.0 C in the voltage range 3.0-4.5 V (vs. Li/Li + ) is comparable to that in the conventional electrolyte, LiPF 6 /EC+DMC. Moreover, the rate capability of the cell with LiTFSI/EMImFSI exceeded that with LiPF 6 /EC+DMC, especially at high rates, probably owing to the low resistance at the electrode/electrolyte interface. These results suggest that EMImFSI is a suitable electrolyte for lithium-ion batteries utilizing an NMC cathode.