Here we demonstrate that the electrochemical properties of Mn based olivine cathode materials can be significantly improved by small amount of co-dopants, Fe and Mg. While nucleation and growth are important in determining the kinetics of a two-phase reaction based olivine electrode, the presence of Fe and Mg in LiMnPO4 framework notably enhances the power capability of a LiMnPO4 electrode providing multiple nucleation sites. The electrochemical activity of an Fe-Mg co-doped Mn olivine cathode material measured by galvanostatic charge/discharge indicates that a discharge capacity of about 140 mAh g(-1) can be obtained at a C/5 rate and this high capacity is retained at even higher current rates (110 mAh g(-1) at 3C), which has yet to be achieved in LiMnPO4 without nucleation enhancers. (C) 2011 The Electrochemical Society. [DOI:10.1149/1.3524260] All rights reserved.