The aluminum current collectors of 11 cycle-life tested Advance Technology Development (ATD) batteries were investigated for evidence of corrosion. The batteries were commercially fabricated and were charge/discharge cycled at temperatures of 25 and 45 degrees C. Our findings clearly show that aluminum current collectors covered with porous cathodes of LiNi0.8Co0.15Al0.5O2 are susceptible to significant crevice corrosion in ethylene carbonate (EC) + ethylmethyl carbonate (EMC) (3:7) with 1.2 M LiPF6. Aluminum current collectors of uncycled ATD cells contain mechanical pits formed during the attachment of the cathode, but with cycling at 25 degrees C there is an increase in percentage of pit area, in the number of pits, in the pit-size-distribution, and in pit depth, which is strong evidence of corrosion of aluminum current collectors of ATD cells. The formation of corrosion pits was confirmed by the presence of corrosion products inside pits and by the pits' surface morphology. Because corrosion of the aluminum current collectors produces corrosion pits, corrosion of mechanical pits, cracks in the aluminum foil, significant concentrations of aluminum (similar to 2,700 ppm) in the ATD electrolytes, and possible mechanical degradation of the cathode, corrosion is expected to significantly effect the battery's power fade and capacity fade. (c) 2007 The Electrochemical Society.