Effect of increasing alkali layer spacing on the performance of O3-NaNi1/3Fe1/3Mn1/3O2cathode materials

O3-Na1-xCax/2Ni1/3Fe1/3Mn1/3O2 (NaCNFMx, x=0, 0.05, 0.1, 0.15) was prepared by doping calcium ions and replacing the sodium sites in the NaNi1/3Fe1/3Mn1/3O2 (NaNFM) material using ball milling spray. XRD, SEM and XPS results demonstrated that the calcium element was successfully embedded in the lattice. The electrochemical performance of NaCNFM0.1 is the best when the doping amount of calcium ion is 0.1. The sodium diffusion coefficient of NaCNFM0.1 cathode material after 3 cycles is 1.67x10- 14 cm2/s. The first specific discharge capacity at 1 C is 121.1 mAh/g. Even at the high current density of 5 C, the 200cycles capacity of 103.6 mAh/g is much higher than NaNFM's 95.2 mAh/g, and the capacity retention rate is as high as 91.5 %. Ex-situ XRD and SEM analyses manifested that the moderate amount of calcium doping improved the stability of the layered structure. These results show that the cathode material has great application potential.