Li2MnO3 powders were synthesized using the solid-state reaction with different Mn sources (Mn3O4 and gamma-MnOOH). The Li2MnO3 powders were characterized by means of XRD, SEM, TEM, and electrochemical testing. The resulting Li2MnO3 powders showed different physical properties and electrochemical reversible capacities depending on their synthetic temperatures and Mn sources. The obtained discharge capacities of two Li2MnO3 materials decreased with increasing calcination temperature. The Li2MnO3 synthesized using Mn3O4 as the starting material showed a high discharge capacity over 160mAh g(-1) after 25th cycle. It was found that the resulting Li2MnO3 powder using Mn3O4 was a composite consisting of monoclinic Li2MnO3, LiMnO2, and LiMn2O4 phases. The reversible discharge capacity of Li2MnO3 in this study originated from the transformation between layered LiMnO2 and cubic LiMn2O4 phases, which was confirmed by the differential capacity, ex situ XRD, and HRTEM results. (C) 2008 Elsevier B.V. All rights reserved.