Effect of lithium and fluorine doping on the electrochemical and thermal stability of LiNi_0.5Mn_1.5O₄ spinel cathode material

Highlights: • Co-doped (Li⁺ and F⁻) Li_1+xNi_0.5Mn_1.5O_4−xF_x (0 ⩽ x ⩽ 0.4) are prepared. • The optimal LiF concentration in the Li_1+xNi_0.5Mn_1.5O_4−xF_x is 0.06 ⩽ x ⩽ 0.2. • Li_1.2Ni_0.5Mn_1.5O_3.8F_0.2 has a better electrochemical and thermal stability. - Abstract: A series of lithium and fluorine substituted Li_1+xNi_0.5Mn_1.5O_4−xF_x (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 Li_1+xNi_0.5Mn_1.5O_4−xF_x 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⁻) LiNi_0.5Mn_1.5O₄ can effectively suppress the exothermic reaction according to the DSC results, which improve the thermal stability of the spinel material