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.