Suppression of multistep phase transitions of O3-type cathode for sodium-ion batteries

O3-type layered oxide cathodes have been widely investigated due to their large reversible capacity and sufficient Na+ reservoirs. However, such materials usually suffer from complex multistep phase transitions along with drastic volume changes, leading to the unsatisfied cycle performance. Herein, we report a Mg/Ti co-doped O3-type NaNi0.5Mn0.5O2, which can effectively suppress the complex multistep phase transition and realize a solid-solution reaction within a wide voltage range. It is confirmed that, the Mg/Ti co-doping is beneficial to enhance structural stability and integrity by absorbing micro-strain and distortions. Thus, the as obtained sample delivers an outstanding cyclic performance (82.3% after 200 cycles at 1 C) in the voltage range of 2.0-4.0 V, and a high discharge capacity of 86.6 mAh/g after 100 cycles within the wide voltage range (2.0-4.5 V), which outperform the existing literatures. This co-doping strategy offers some insight into high performance O3-type cathode for sodium ion batteries.