Abstract: As one of the most promising cathode materials for high energy density lithium ion batteries, LiNi_0.6Co_0.2Mn_0.2O₂ with high reversible capacity suffers poor cycling performances, especially at high cutoff potentials. To address this challenge, in this study, an atomic layer deposition is utilized to design controllable MgO coating layers onto LiNi_0.6Co_0.2Mn_0.2O₂ cathode material. It is confirmed that the optimized LiNi_0.6Co_0.2Mn_0.2O₂ cathode shows an improved electrochemical performance comparing with the pristine material at the cutoff potentials of 4.5 V as well as 4.7 V. After 100 cycles, the LiNi_0.6Co_0.2Mn_0.2O₂ with MgO coating displays the reversible capacities of 157 mAh·g⁻¹ and 158 mAh·g⁻¹ at the cutoff potential of 4.5 V and 4.7 V, respectively, which is higher than those of the pristine one (131 mAh·g⁻¹ and 144 mAh·g⁻¹). This study demonstrates that the ALD derived MgO coating layer shows some promising potentials to improve LiNi_0.6Co_0.2Mn_0.2O₂ performance for lithium ion batteries. This is mainly due to the effective protection of MgO layer to the material surface, that is, the MgO coating can stabilize the interface and block the metal ion dissolution by reducing the direct connection between LiNi_0.6Co_0.2Mn_0.2O₂ and electrolyte.