The corrosion behavior of Al foil as the current collector for lithium-ion batteries is studied by linear-sweep thermammetry. The onset temperature for Al pitting corrosion depends on Li salt that is dissolved in an ionic liquid solvent; lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)< lithium bis(perfluoroethanesulfonyl)imide (LiBETI) < LiPF6 < LiBF4. With LiBF4, no corrosion current is observed until 110 degrees C. X-ray photoelectron spectroscopy study reveals that this Al surface is covered by Al-F compound (presumably AlF3). Due to the formation of a highly passivating AlF3 layer in this electrolyte, the high voltage LiNi0.5Mn1.5O4 positive electrode coated on Al foil can be successfully cycled at 65 degrees C without electrode failure. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3432256] All rights reserved.