Effects of Cl doping on the structural and electrochemical properties of high voltage LiMn1.5Ni0.5O4 cathode materials for Li-ion batteries

LiMn1.5Ni0.5O4 and LiMn1.5Ni0.5O3.9Cl0.1 are prepared by a solution-based process to investigate the influences of Cl doping on the structural and electrochemical properties of high voltage LiMn1.5Ni0.5O4 cathode materials for Li-ion batteries. LiMn1.5Ni0.5O3.9Cl0.1 features an improved cyclic performance at 30 °C and 55 °C compared with LiMn1.5Ni0.5O4, which originates from the enhanced structural stability by formation of strong Mn–Cl and Ni–Cl bonds revealed by XPS analysis. The improvement in the rate capability of LiMn1.5Ni0.5O3.9Cl0.1 is attributed to the facilitated Li-ion diffusion in the lattice, due primarily to the larger ionic radius of Cl than that of O. From the GITT analysis, it is revealed that the Li-ion diffusivity of LiMn1.5Ni0.5O3.9Cl0.1 is improved about 2 times compared with that of LiMn1.5Ni0.5O4. The improved Li-ion diffusivity in the lattice is assigned to the increase in the lattice constant of LiMn1.5Ni0.5O3.9Cl0.1 compared with that of LiMn1.5Ni0.5O4 by the doping of Cl.