A multi-phase Li-Mn-O nanocomposite, xLi(4)Mn(5)O(12)center dot yLiMn(2)O(4)center dot zLi(2)MnO(3), is synthesized via an oxidation reaction by controlling the molar ratio of Li and Mn in the LixMnyOz center dot nH(2)O precipitate. Synchrotron X-ray diffraction and high-resolution transmission electron microscopy confirm the constitution of the multi-phase nanocomposite as Li4Mn5O12, LiMn2O4, and Li2MnO3. The electrochemical measurements demonstrate that this nanocomposite cathode exhibits a discharge capacity of 196.8 mAh/g at 14.2 mA/g of current density with the characteristic profiles typical of layered structure as well as spinel phases. The cycle performance of the sample during extended cycling shows stable discharge capacities without any drastic capacity decay. The absence of capacity fading during cycling in the high voltage range of 2.0-4.8 V confirms that the prepared nanocomposite with multi-phase is structurally stable for lithium insertion/de-insertion process. (C) 2017 The Electrochemical Society. All rights reserved.