Effect of Nb and F Co-doping on LiMnNiCoO Cathode Material for High-Performance Lithium-Ion Batteries.

The LiMnNbCoNiOF ( = 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 LiMnCoNiO, 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 LiMnNbCoNiOF shows suppressed voltage fade and higher capacity retention of 98.1% after 200 cycles at rate of 1 C. The replacement of O by the strongly electronegative F is beneficial for suppressed the structure change of LiMnO from the eliminating of oxygen in initial charge process. Therefore, the initial coulombic efficiency of doped LiMnNbCoNiOF gets improved, which is higher than that of pure LiMnCoNiO. In addition, the Nb and F co-doping can effectively enhance the transfer of lithium-ion and electrons, and thus improving rate performance.