The aluminum current collectors from six ATD cells that were commercially fabricated and cycle-life (charge/discharge) tested at 25°C were microscopically inspected for evidence of corrosion. The results clearly show that aluminum covered with porous cathodes of LiNi{sub}0.8Co{sub}0.15Al{sub}0.5O{sub}2 of cycle-life ATD cells cycled at 25°C is susceptible to significant underdeposit corrosion in LiPF{sub}6-containing battery electrolytes. Aluminum current collectors of uncycled ATD cells contain mechanical pits formed during the attachment of the cathode, but with cycling at 25°C there is an increase in percentage pit area, in the number of pits, in pit-size-distribution, and in pit depth, which is a strong evidence of corrosion of Al current collectors of ATD cells. The formation of corrosion pits, corrosion of mechanical pits, and the non negligible amount of aluminum that was found in the electrolytes (～2700ppm) of cycle-life tested ATD cells explain the significant contribution of corrosion to the power fade and capacity fade and the possibility of mechanical degradation of the cathode as well.
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