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

Lithium-excess layered cathode materials Li[Li 0.2 Mn 0.54   −   x Sm x Co 0.13 Ni 0.13 ]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[Li 0.2 Mn 0.54 Co 0.13 Ni 0.13 ]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[Li 0 . 2 Mn 0.54 Co 0 . 13 Ni 0.13 ]O 2 structure. The Li[Li 0.2 Mn 0.51 Sm 0.03 Co 0.13 Ni 0.13 ]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[Li 0·2 Mn 0.51 Sm 0.03 Co 0.13 Ni 0.13 ]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.