Spectroscopic studies of the structural properties of Ni substituted spinel LiMn2O4

Microstructure and local structure of spinel LiNixMn2 − xO4 (x = 0, 0.1 and 0.2) were studied using X-ray diffraction (XRD) and a combination of X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge spectroscopy (XANES) and Raman scattering with the aim of getting a clear picture of the local structure of the materials responsible for the structural stability of LiNixMn2 − xO4. XRD study showed that Ni substitution caused the changes of the materials’ microstructure from the view of the lattice parameter, mean crystallite size, and microstrain. XPS and XANES studies showed the Ni oxidation state in LiNixMn2 − xO4 was larger than + 2, and the Mn oxidation state increased with Ni substitution. The decrease of the intensity of the 1s → 4pz shakedown transition on the XANES spectra indicated that Ni substitution suppressed the tetragonal distortion of the [MnO6] octahedron. The Mn(Ni)–O bond in LiNixMn2 − xO4, which is stronger than the Mn–O bond in LiMn2O4 was responsible for the blue shift of the A1g Raman mode and could enhance the structural stability of the [Mn(Ni)O6] octahedron.