Li1.2-xNaxMn0.54Co0.13Ni0.13O2 with nano size is synthesized with a confinement method. Li1.2-xNaxMn0.54Co0.13Ni0.13O2 (x = 0.05, 0.10 and 0.20) presents enhanced initial charge-discharge efficiency, rate capability and cycling stability in comparison with Li1.2Mn0.54Co0.13Ni0.13O2. At 0.1C (25 mA g (1)), the initial charge-discharge efficiency is increased from 76% of Li1.2Mn0.54Co0.13Ni0.13O2 to 90% of Li1.1Na0.1Mn0.54Co0.13Ni0.13O2; and the capacity retention in the 20th cycle versus the initial cycle is improved from 31% for Li1.2Mn0.54Co0.13Ni0.13O2 to 88% for Li1.1Na0.1Mn0.54Co0.13Ni0.13O2; at 500 mA g (1), Li1.1Na0.1Mn0.54Co0.13Ni0.13O2 has a discharge capacity of 128 mAh g (1), while the Na-free sample Li1.2Mn0.54Co0.13Ni0.13O2 only delivers a lower discharge capacity of 54 mAh g (1). The superior electrochemical performance of Li1.2-xNaxMn0.54Co0.13Ni0.13O2 (x = 0.05, 0.1 and 0.2) is mainly due to sodium doping, which can enlarge the interslab distance and stabilize the crystal structure. (C) 2016 Elsevier Ltd. All rights reserved.