Synthesis and performance of fluorine substituted Li1.05(Ni0.5Mn0.5)0.95O2−xFx cathode materials modified by surface coating with FePO4

The F-doped layered cathode materials Li1.05(Ni0.5Mn0.5)0.95O2−xFx(0 ≤ x ≤ 0.1) with ball-like shape were successfully synthesized by carbonate co-precipitation method, followed by a high temperature calcination process. The effects of fluorine content on the crystal structure, morphology and electrochemical performance were extensively investigated. The XRD results reveal that all the materials synthesized have typical hexagonal structure without impurity. Fluorine-doped materials could have improved cycling performance compared with Li1.05(Ni0.5Mn0.5)0.95O2, and Li1.05(Ni0.5Mn0.5)0.95O1.95F0.05 shows the best electrochemical property. In addition, 3 wt% FePO4-coated Li1.05(Ni0.5Mn0.5)0.95O1.95F0.05 has significantly improved rate capability and better thermal stability compared with pristine sample. Electrochemical impedance spectroscopy (EIS) measurements reveal that both fluorine substitution and FePO4 coating could suppress the increase of charge transfer resistance with cycling. Overall, the combination of fluorine doping and FePO4 coating was effective in improving both cycling performance and rate capability of Li1.05(Ni0.5Mn0.5)0.95O2.