Structural and defect study of LiMn2O4 formation

The LiMn2O4 formation from MnO and Li2CO3 mixtures with lithium cationic fraction 0.31 less than or equal to x less than or equal to 0.40 was studied by structural profile refinement from X-ray data, thermal (TGA and DSC) measurements and scanning electron microscopy (SEM) observations. Quantitative phase analysis, structural and microstructural parameters and composition of the coexisting phases were obtained. Different behaviours were observed in the composition ranges 0.33 less than or equal to x less than or equal to 0.35 and x greater than or equal to 0.37. In the former range only the stoichiometric spinel phase was obtained, in the latter, in addition to the Li2MnO3 compound, two spinel phases could be considered: I) LiMn2O4 stoichiometric spinel; II) Li1+yMn2-yO4 (0.11 less than or equal to y less than or equal to 0.23), a non-stoichiometric phase whose small particle size resulted practically independent of the initial composition and annealing temperature. Such a conclusion was supported also by SEM observations. The relative abundance of phase II increased with increasing lithium content and with decreasing temperature.