Tuning oxygen release of sodium-ion layered oxide cathode through synergistic surface coating and doping

Layered transition metal oxides have the greatest potential for commercial application as cathode materials for sodium-ion batteries. However, transition metal oxides inevitably undergo an irreversible oxygen loss process during cycling, which leads to structural changes in the material and ultimately to severe capacity degradation. In this work, using density function theory (DFT) calculations, the Ni-O bond is revealed to be the weakest of the M-O bonds, which may lead to structural failure. Herein, the synergistic surface CeO2 modification and the trace doping of Ce elements stimulate oxygen redox and improve its reversibility, thus improving the structural stability and electrochemical performance of the material. Theoretical calculations prove that Na0.67Mn0.7Ni0.2Co0.1O2 (MNC) obtains electrons from CeO2, avoiding destruction of the Ni-O bond by over-energy released during the charging process and inhibiting oxygen loss. The capacity retention was 77.37% for 200 cycles at 500 mA g-1, compared to 33.84% for the unmodified Na0.67Mn0.7Ni0.2Co0.1O2. Overall, the present work demonstrates that the synergistic effect of surface coating and doping is an effective strategy for realizing tuning oxygen release and high electrochemical performance.