Crystallization of LiMn 2O 4 observed with high temperature X-ray diffraction

We investigated the formation of LiMn ₂O ₄ phases by calcinating a stoichiometric mixture of Li ₂CO ₃ and various manganese compounds with high temperature X-ray diffraction (HT-XRD) technique to understand the influence of starting materials on the electrochemical performance. XRD measurements were carried out during heating processes from room temperature to 700 °C. In case of Li ₂CO ₃/electrolytic manganese dioxide and Li ₂CO ₃/MnCO ₃ mixtures used as starting materials, Li _0.33MnO ₂ phase and low crystalline phase, respectively, appeared as intermediate products during heating process followed by the crystallization into the spinel. HT-XRD observation confirmed that the LiMn ₂O ₄ phase was directly formed from starting Li ₂CO ₃/Mn ₂O ₃ and Li ₂CO ₃/Mn ₃O ₄ mixtures. The reactivity of the mixture, meant by the lower reaction temperature between Li and Mn compounds and the faster evolution of Li-Mn-O phase, depended on manganese compounds. The purity and stoichiometry of spinel type LiMn ₂O ₄ was not achieved only by the higher reactivity. From these results, the dependence of reversible capacities and cycleability of synthesized LiMn ₂O ₄s on the formation process which varied with the starting materials was discussed.