The monoclinic Li2MnO3 is electrochemically inactive for lithium intercalation at voltages lower than 4.4 V vs. Li+/Li-0. In order to activate Li2MnO3, magnesium has been incorporated in the lithium site of the structure which resulted in a mixture of active phases capable of cycling in the 2.8 to 4.8 V vs. Li+/Li-0 voltage range. Li2MnO3, Li1.5Mg0.25MnO3, Li1.0Mg0.50MnO3 and Li0.5Mg0.75MnO3 compositions were synthesized by the modified Pechini method and formulated based on the oxidation state of magnesium and lithium. The compounds were characterized using XRD, XPS, SEM, BET and tap density. The XRD patterns for Li1.5Mg0.25MnO3, Li1.0Mg0.50MnO3 and Li0.5Mg0.75MnO3 indicated the presence of monoclinic/spinel phases. Li0.5Mg0.75MnO3 showed ideal values of tap density vs. surface area among all the Mg-substituted compounds. X-ray photoelectron spectroscopy of Mn 2p orbital showed a decrease in the oxidation state of manganese for Li1.0Mg0.50MnO3 and Li0.5Mg0.75MnO3, while the change in binding energy for Li1.5Mg0.25MnO3 was not significant. The cyclic voltammetry and charge/discharge tests showed an increase in capacity and better stability for the Li1.0Mg0.50MnO3 (80 mAh g(-1)) and Li0.5Mg0.75MnO3 (112 mAh g(-1)) compositions. (C) 2017 The Electrochemical Society. All rights reserved.