Effect of lithium and fluorine doping on the electrochemical and thermal stability of LiNi0.5Mn1.5O4 spinel cathode material

A series of lithium and fluorine substituted Li1+xNi0.5Mn1.5O4−xFx (0 ⩽ x ⩽ 0.4) spinel powders have been synthesized by a solid-state method. The effects of LiF content on structural, electrochemical and thermal properties are extensively investigated. The XRD patterns show that impurity arises when x ⩾ 0.3. FTIR results indicate that the cation disordering degree increases with an increasing in content of the co-doping with Li and F. The LiF concentration is optimized in the range of 0.06 ⩽ x ⩽ 0.2 in which the cyclic stability and rate capability of the Li1+xNi0.5Mn1.5O4−xFx spinels are significantly improved. Moreover, TEM images reveal that co-doped (Li+ and F−) particles form a smooth and uniform surface film, which mitigate the interaction of active materials and electrolyte solution as well as improve cycling stability. Besides, the thermal property of the co-doped (Li+ and F−) LiNi0.5Mn1.5O4 can effectively suppress the exothermic reaction according to the DSC results, which improve the thermal stability of the spinel material.