Effects of Ni Doping on MnO6 Octahedron in LiMn2O4

LiNixMn2-xO4 (x ≤ 0.5) powders were synthesized using a sol−gel technique. It was found that partial Ni atoms occupy the 8a sites in heavy doped LiNixMn2-xO4 via X-ray diffraction. XPS results showed an increase and a decrease in the average valence state of Mn and Ni ions, respectively, with the nickel content. Five Raman modes of LiNixMn2-xO4 were observed. The A1g band was observed being shifted to higher frequency for x ≤ 0.2 and shifted to lower frequency for x > 0.2. It was indicated that the most rigid MnO6 octahedron occurs at x = 0.2. MnO6 octahedron in LiNi0.2Mn1.8O4 possesses the strongest rigidity with respect to the other LiNixMn2-xO4 (x < 0.5 and ≠ 0.2).