Understanding the enhanced electrochemical performance of samarium substituted Li[Li0.2Mn0.54 − xSmxCo0.13Ni0.13]O2 cathode material for lithium ion batteries

• The Sm-substituted electrode shows elevated electrochemical performance.
• Enlarged Li layer space, inhibited oxygen release and better electrical conductivity are achieved.
• The rare earth elements series are hoped to further used on other layered cathode materials.

Lithium-excess layered cathode materials Li[Li0.2Mn0.54 − xSmxCo0.13Ni0.13]O2 (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]O2 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]O2 structure. The Li[Li0.2Mn0.51Sm0.03Co0.13Ni0.13]O2 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[Li0·2Mn0.51Sm0.03Co0.13Ni0.13]O2 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.