Surface modification by fluorine doping to increase discharge capacity of Li1.2Ni0.2Mn0.6O2 cathode materials

Anion doping is considered as an effective method to tap the potential of Li-rich materials to obtain more discharge capacity. Here, we prepare fluorine-doped Li1.2Ni0.2Mn0.6O2 materials by a low-temperature secondary sintering. Rietveld refinements of XRD show an increase in lattice parameters and indicate a wider Li+ diffusion channel after fluorine doping. From TEM and HRTEM images, it is observed that the fluorine-doped sample displays a more pronounced layered appearance, and partial lattice fringes are slightly curved which may be caused by the substitution of F for O to break the symmetry of MnO6 octahedron. The fitting results of XPS show that Mn is partially oxidized and the local electronic environment of O changes. The best one shows a discharge capacity of 288 mAh/g at 0.1 C with a Coulombic efficiency of 95.9% in the first lap. And it performs a capacity retention of 91.0% after 100 cycles at 0.2 C.