Recently, lithium bi-metal phosphates (LiM'M '' PO(4)) have been synthesized for use as cathode materials in order to increase cell voltages and electrical performances. In this work, we have substituted Mn(2+) at the 4c site of LiFePO(4) to prepare the lithium bi-metal phosphate LiMn(0.25)Fe(0.75)PO(4) and have found that it greatly enhances the cell voltage. At a 0.05 C discharge rate, the cell capacity was about 153 mAhg(-1) and the average working voltage rose to 3.53 V due to the Mn substitution. However, the capacity and working voltage both decrease as the discharge rate increases. By in-situ metal K-edge absorption analysis, it reveals that the substituted metal Mn(2+) does not work completely at a higher discharge rate, due to poor electrical conductivity and a serious Jahn-Teller effect. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.
