A study of the corrosion of Al, used as a current collector for the cathode of rechargeable lithium batteries, has been carried out using the electrochemical quartz crystal microbalance (EQCM). An aluminum film was highly corroded in 1 M LiTFSI (lithium trifluorosulfonimide (LiTFSI), LiN(SO2CF3)(2))/EC + DMC electrolyte at 2-5 V versus Li/Li+ with the formation of large pits, while the corrosion was clearly suppressed by adding LiBF4 salt into the imide electrolyte. Depression of corrosion on adding LiBF4 was attributed to the formation of a stable passive layer on the surface of aluminum due to the reaction of aluminum with electrolyte and the decomposition of electrolyte solvent at high potentials. The resulting data may help clarify the corrosion mechanism of aluminum metal in imide electrolyte and give insight into enhancing the performance of lithium ion batteries. (C) 2003 Elsevier Ltd. All rights reserved.