Preparation and electrochemical performance of LiNi0.5Mn0.5O2-xFx (0 ≤ x ≤ 0.04) cathode material synthesized with hydroxide co- precipitation for lithium ion batteries

Layered LiNi0.5Mn0.5O2-xFx (0 <= x <= 0.04) has been successfully synthesized via hydroxide co-precipitation method and solid-state reaction method. The crystal structure and morphology of the materials were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. It is found that the LiNi0.5Mn0.5O1.96F0.04 synthesized at 950 degrees C for 30 h in air atmosphere show the smooth and regular structure in the particle size range of 0.77-1.13 mu m. The initial discharge capacity was 176.2 mAh g(-1) between 2.8 and 4.6 V at 0.2 C ratio (1 C = 200 mAh g(-1)). The reversible capacity was 87.9% of the initial discharge capacity at cut-off voltage of 4.60 V after 50 cycles at 0.2 C, 0.5 C and 1.0 C ratio. The lithium ion diffusion coefficient of LiNi0.5Mn0.5O1.96F0.04 was 4.34 x 10(-13) cm(2) s(-1), which was much greater than that of the LiNi0.5Mn0.5O2. The excellent electrochemical performance could be attributed to its lower Li/ Ni exchange ratio and larger lithium ion diffusion coefficient. It was demonstrated that doping F process was a useful and efficient approach to reduce the cation mixing and improve the poor rate performance of LiNi0.5Mn0.5O2 material. (C) 2013 Elsevier B. V. All rights reserved.