Effect of Nb and F Co-doping on Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ Cathode Material for High-Performance Lithium-Ion Batteries

The Li_1.2Mn_0.54-xNb_xCo_0.13Ni_0.13O_2-6xF_6x (x = 0, 0.01, 0.03, 0.05) is prepared by traditional solid-phase method, and the Nb and F ions are successfully doped into Mn and O sites of layered materials Li_1.2Mn_0.54Co_0.13Ni_0.13O₂, respectively. The incorporating Nb ion in Mn site can effectively restrain the migration of transition metal ions during long-term cycling, and keep the stability of the crystal structure. The Li_1.2Mn_0.54-xNb_xCo_0.13Ni_0.13O_2-6xF_6x shows suppressed voltage fade and higher capacity retention of 98.1% after 200 cycles at rate of 1 C. The replacement of O^2- by the strongly electronegative F^- is beneficial for suppressed the structure change of Li₂MnO₃ from the eliminating of oxygen in initial charge process. Therefore, the initial coulombic efficiency of doped Li_1.2Mn_0.54-xNb_xCo_0.13Ni_0.13O_2-6xF_6x gets improved, which is higher than that of pure Li_1.2Mn_0.54Co_0.13Ni_0.13O₂. In addition, the Nb and F co-doping can effectively enhance the transfer of lithium-ion and electrons, and thus improving rate performance.