Improved cycling stability of P2-type Na0.71Co0.96O2 cathode material by optimizing Ti doping

The electrode materials with long cycle life are important for the large-scale application of sodium ion batteries. In this work, P2-type Na 0.71 Co 0.96- x Ti x O 2 ( x  = 0, 0.057, 0.073, 0.09) were synthesized by molten-salt method. The Ti doping content could influence the crystallographic unit cell volume, particle size, oxygen vacancies, and surface charge density of those samples. When x  = 0.073, the P2-type Na 0.71 Co 0.96- x Ti x O 2 ( x  = 0.073) exhibits superior reversible capacity and rate performance due to the appropriate synergistic effect. In particular, the initial discharge capacity of NCTO-0.073 is about 118.5 mAh g −1 at 100 mA g −1 . Even the current density gets to 1000 mA g −1 , the initial discharge capacity remains 71.7 mAh g −1 after 1000 cycling with the capacity retention of 67.90%. The electrochemical kinetics analysis further prove that the P2-type Na 0.71 Co 0.96- x Ti x O 2 ( x  = 0.073) owns outstanding electrical conductivity and fast sodium ion diffusion behavior to promote the electrochemical reaction during the charging/discharging. These results will contribute to the industrialized application of stable high-performance cathodes for sodium ion batteries.