Structural and electrochemical properties of LiNi1/3Mn1/3Co1/3O2−xFx prepared by solid state reaction

A series of LiNi1/3Mn1/3Co1/3O2−xFx (0 ≤ x ≤ 1) compounds was prepared by a solid state reaction and their characteristics were investigated by XRD, SEM, XPS, EIS, and charge–discharge test. The substitution of oxygen by fluorine produces change in the valences of the transition metal ions, thereby induces a complex change in the lattice parameters. Moreover, the fluorine doping of the LiNi1/3Mn1/3Co1/3O2 can promote the grain size growth and improve its crystallinity. The substituted samples with a low fluorine content can stabilize the interface between the surface layer of the active particles and the electrolyte after cycling, which is probably related to the improvement of the cyclic performance. A high fluorine content introduction into LiNi1/3Mn1/3Co1/3O2 significantly decreases its electrochemical properties, which is probably due to the formation of a new unstable interface as well as a structural instability caused by the nonequivilent substitution.