We evaluated the charge-discharge behavior of a graphite electrode in a 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMImFSI) ionic liquid. According to the charge-discharge tests, the graphite negative electrode exhibited a high rate of performance in LiTFSI/EMImFSI (TFSI- = bis(trifluoromethylsulfonyl)imide) in the voltage range of 0.005-1.5 V (vs. Li/Li+), and the performance was comparable to that in a conventional organic solution-based electrolyte, LiPF6/EC+DMC. Moreover, the addition of LiBOB (=lithium bis(oxalato)borate) improved the rate capability and low-temperature operation of the graphite negative electrode, most likely owing to the low-resistivity solid electrolyte interface (SEI) derived from LiBOB. These results suggest that EMImFSI is a suitable electrolyte for lithium-ion batteries utilizing graphite negative electrodes and that optimization of the electrolyte composition with an additive can improve battery performance. (C) 2012 Elsevier B.V. All rights reserved.