Abstract: Because of its good electrochemical performance and high operating voltage around 4.7 V, LiNi_0.5Mn_1.5O₄ spinel has become one of the most promising high voltage cathode materials for lithium ion batteries with high energy density. In this paper, we prepared LiNi_0.5Mn_1.5O₄ cathode materials through spray drying assisted annealing process with different heat treating conditions, the effect of heat treatment conditions on the structure and electrochemical performances was investigated. The crystal structures of the prepared LiNi_0.5Mn_1.5O₄ materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transformed infrared spectroscopy (FT-IR). The in situ synchrotron X-ray diffraction technique was carried out to study the online phase transition of LiNi_0.5Mn_1.5O₄ spinel during cycling. It has been found that the prepared LiNi_0.5Mn_1.5O₄ powders show phase-pure cubic spinel of Fd-3m structure. Its electrochemical performances were tested at different charge/discharge rates between the potential limit of 3.5~5.0 V, and the initial discharge capacity of the LiNi_0.5Mn_1.5O₄ spinel attained at 132.0 mA·h·g^-1, and the columbic efficiency at first cycle is 93.48%, and the electrochemical performances of the prepared materials are excellent.From the in situ XRD patterns and charge-discharge profile, it can be found that four phase transitions existed for LiNi_0.5Mn_1.5O₄ spinel during charge process, the phase transition from tetrahedral to cubic is reversible in the lithium insertion and extraction process.

Key words: LiNi0.5Mn1.5O4, cathode material, electrochemical characteristic, phase transition, in situ XRD