Ultrathin atomic layer deposition (ALD) coatings enhance the performance of lithium-ion batteries (LIBs). Previous studies have demonstrated that LiCoO2 cathode powders coated with metal oxides with thicknesses of similar to 100 to 1000 angstrom grown using wet chemical techniques improved LIB performance. In this study, LiCoO2 powders were coated with conformal Al2O3 ALD films with thicknesses of only similar to 3 to 4 angstrom established using two ALD cycles. The coated LiCoO2 powders exhibited a capacity retention of 89% after 120 charge-discharge cycles in the 3.3-4.5 V (vs Li/Li+) range. In contrast, the bare LiCoO2 powders displayed only a 45% capacity retention. Al2O3 ALD films coated directly on the composite electrode also produced improved capacity retention. This dramatic improvement may result from the ultrathin Al2O3 ALD film acting to minimize Co dissolution or reduce surface electrolyte reactions. Similar experiments with ultrathin ZnO ALD films did not display enhanced performance. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3258274] All rights reserved.