Achieving multiscale structural optimization of O3-NaNi0.5Mn0.5O2 cathode via stepwise calcination and surface modification for high-performance sodium-ion storage

O3-NaNi0.5Mn0.5O2 cathode with high reversible capacity are promising cathode candidates for Na-ion batteries. However, the poor cycling performance caused by layered structure collapse and side reaction with the electrolyte during charging and discharging limits the practical application of NaNi0.5Mn0.5O2. Here, we propose a synergistic strategy of stepwise calcination and surface modification to enhance structural stability and electrochemical performance of NaNi0.5Mn0.5O2 cathode. Firstly, the crystallinity and the structural stability of the synthesized cathode have been optimized by unique stepwise calcination, in which Ni0.5Mn0.5(OH)2 precursor was calcined separately at 750 degrees C for 20 h. The spacing of Na layer is enlarged and the diffusion rate of Na is increased. In addition, the interface side reactions between cathode and electrolyte are suppressed by coupling with the TiO2 surface coating, improving cycle performance while increasing capacity. As expected, the optimized sample presents a high specific capacity of 145.8 mAh & sdot;g- 1 with a high capacity retention rate of 87.4 % after 100 cycles at 1C. This work provides a novel way to develop O3 layered cathode materials for sodium-ion batteries with high capacity and long cycle life.