Cathode current collectors made of aluminum are corroded by LiN (SO2CF3)(2)/ethylene carbonate + dimethyl carbonate (1: 1 in volume ratio) electrolyte above 3.7 V. Therefore, the electrolyte cannot be used for 4 V lithium rechargeable batteries. By contrast, LiN (SO2CF3)(2)/methyl difluoroacetate (CHF2COOCH3, MFA) electrolyte showed good inhibition of aluminum corrosion, and a Li/LiCoO2 cell with an aluminum cathode current collector exhibited good cycle performance when the LiN (SO2CF3)(2)/MFA electrolyte was used. X-ray photoelectron spectroscopy of the aluminum surface treated by LiN (SO2CF3)(2)MFA electrolyte showed that the inhibition of corrosion derives from a passivation film made of an organic compound on the aluminum surface. (c) 2005 The Electrochemical Society. All rights reserved.