The enhanced electrochemical performance of LiNi0.6Co0.2Mn0.2O2 cathode materials by low temperature fluorine substitution

Layered oxy-fluoride LiNi0.6Co0.2Mn0.2O2−zFz (0 ≤ z ≤ 0.06) cathode materials have been synthesized by a low temperature (450 °C) fluorination with NH4F of the corresponding LiNi0.6Co0.2Mn0.2O2 oxides that were synthesized by hydroxide co-precipitation method. The effect of fluorine content on the structure and electrochemical performance of the LiNi0.6Co0.2Mn0.2O2−zFz has been extensively studied. The XRD results reveal that LiNi0.6Co0.2Mn0.2O2−zFz (0 ≤ z ≤ 0.06) has typical hexagonal structure without impurity. The composition analysis and XPS verify fluorine incorporation in the particle. The electrochemical results indicate that the initial discharge capacity slightly decreases with increasing the content of fluorine. However, cycling performance and rate capability are improved by the fluorine substitution. In addition, after stored at 90 °C for 5 h in fully charged state, fluorine substituted materials exhibit better cycling performance than pristine materials. Electrochemical impedance spectroscopy shows that fluorine substitution can reduce the charge transfer resistance. Overall, fluorine substitution has a positive effect on the electrochemical performance of layered LiNi0.6Co0.2Mn0.2O2.

► A low temperature process has been used to synthesize fluorine substituted material. ► Fluorine substitution plays a positive effect on the electrochemical performance. ► Fluorine substitution enhanced storage performance. ► Fluorine substituted materials have lower charge transfer resistance than pristine materials.