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

• We have synthesized the layered LiNi0.5Mn0.5O2−xFx (0 ⩽ x ⩽ 0.04) by hydroxide co-precipitation method.
• The structure, morphology and electrochemical performance of LiNi0.5Mn0.5O2 are influenced by F doping effect.
• The cations mixing of pure LiNi0.5Mn0.5O2 decreases and Li+ diffusion coefficient increases with doping F.
• The reversible capacity of LiNi0.5Mn0.5O1.96F0.04 is 155.0 mAh g−1 after 50 cycles at 0.2 C, 0.5 C and 1.0 C ratios between 2.8 and 4.6 V.

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 °C for 30 h in air atmosphere show the smooth and regular structure in the particle size range of 0.77–1.13 μm. 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 × 10−13 cm2 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.