Lithium-excess layered cathode materials Li[Li0.2Mn0.54-xSmxCo0.13Ni0.13]O-2 (x = 0, 0.01, 0.03, 0.05) with different quantities of Sm were synthesized by the coprecipitation-calcination method. The rare earth element samarium (Sm) was introduced into the structure of Li[Li0.2Mn0.54Co0.13Ni0.13]O-2 as the replacement at Mn sites. The refinement unit cell parameters from the X-ray powder diffraction patterns illustrate the doping of Sm facilitates enlarging the lithium ions diffusion passageway space of the Li[Li0.2Mn0.54Co0.13Ni0.13]O-2 structure. The Li[Li0.2Mn0.54-xSm0.03Co0.13Ni0.13]O-2 electrode presented the best electrochemistry properties. The initial discharge capacity is 287.5 mAh g(-1) and the initial coulombic efficiency increases from 81.31% to 85.34% with a constant current density of 12.5 mA g(-1), which can be attributed to the suppression of the oxygen release from the structure at the initial charge-discharge process. The Li[Li0.2Mn0.51xSm0.03Co0.13Ni0.13]O-2 electrode delivers 236.1 mAh g(-1) after 40 cycles and the capacity retention ratio is 82.12% while only 206.8 mAh g(-1) and 70.85% are obtained after 40 times of cycling for the pristine electrode. The Nyquist plots indicate that the electrical conductivity and interfacial electrochemical reaction activity increase as well. (C) 2016 Elsevier B.V. All rights reserved.