Ultrathin Al2O3 is directly deposited on LiNi0.5Co0.2Mn0.3O2 (NCM523) composite electrodes by atomic layer deposition (ALD). After 4 ALD cycles, the coated cathode exhibits significantly improved cycling performance and thermal stability, especially at high working voltage. The capacity retention of the coated cathode is 76.8% after 30 cycles in the voltage range of 2-4.8 V, compared to 58.4% of pristine cathode. The exothermic peak in differential scanning calorimetry (DSC) analysis, corresponding to the reactions between delithiated electrode and electrolyte, is also delayed after cycling. The improvement is attributed to the reduced charge transfer resistance and enhanced Li ion diffusivity, as the Al2O3 coating may suppress the side reactions between electrode and electrolyte, and inhibit the oxygen release under high operating voltage. (C) 2016 Elsevier Ltd. All rights reserved.