Effects of fluorine substitution on the electrochemical performance of layered Li-excess nickel manganese oxides cathode materials for lithium-ion batteries

Li[Li1/6Ni1/4Mn7/12]O2−xFx (x = 0, 0.025, 0.05, 0.075, 0.1) as the cathode materials for rechargeable lithium batteries have been synthesized via the co-precipitation method followed by a high-temperature solid-state reaction. Field emission scanning electron microscopy images exhibit that fluorine substitution catalyzes the growth of the primary particles. Although the initial discharge capacity decreases as the fluorine content increasing, the fluorine substituted materials present significant improvement in the cycling performance. Among the synthesized materials, Li[Li1/6Ni1/4Mn7/12]O1.95F0.05 exhibits excellent high temperature (50 °C) cycling performance with a capacity retention of 93.7% after 30 cycles while the bare Li[Li1/6Ni1/4Mn7/12]O2 cathode exhibited only 73.7%.