This study investigated the annealing of atomic layer deposited (ALD) Al2O3 coated onto Li-ion battery cathodes to enhance their electrochemical properties. LiNi0.5Mn0.3Co0.2O2 (NMC) cathode powders were coated with 5 ALD cycles at 100 °C, annealed between 300 and 700 °C, cast into electrode sheets and assembled into coin cells. Cells were characterized using charge-discharge cycling, electrochemical impedance spectroscopy, pre-casting and postmortem X-ray photoelectron spectroscopy, and charge endpoint slippage measurement. Diffusion of Al into bulk NMC was observable at ≥500 °C, and extent of diffusion increased with increasing temperature. Un-annealed ALD-coated cathodes showed exceptional capacity retention at high charge-discharge rates, while annealed cells showed recovery of initial charge capacity lost upon ALD coating. High quantities of LiF forming surface species were detected in cells annealed at 500 °C. This study approaches post-deposition annealing as a parameter that may be used to explore the electrochemical properties of ALD-coated battery cathodes.