Preparation, physical and structural characterization of LiMnO2 samples with variable cationic disorder

Abstract

Orthorhombic LiMnO₂ samples, synthesized at high temperatures from a mixture of LiOH·H₂O and Mn₂O₃ under a reducing atmosphere, have been fully characterized. The morphology showed that important differences exist between two sets of materials: A-type materials prepared with a deficiency of LiOH with respect to the LiMnO₂ stoichiometric composition and B-type materials prepared with an excess of LiOH. Bulk density variations were interpreted in terms of the occurrence of several lithium and/or manganese salt impurities. From Rietveld refinements, and contrary to the previously described LiMnO₂ structures, the present LiMnO₂ samples exhibit a cationic disorder on the lithium and manganese sites, with occupancy variations ranging from 3 to 12%. Finally, the frequently occurring abnormal widening of the second diffraction line could be modelled and attributed to the mixing of a regular diffraction peak of the phase under study [the (110) reflection] and of some poorly crystallized unreacted Mn₂O₃. These structural results can be used to explain the electrochemical behaviour of the samples when employed as cathodes in rechargeable lithium batteries.