We report electrochemical studies of high voltage cathodes composed of lithium rich "layered-layered" material having the nominal composition Li1.2Mn0.525Ni0.175Co0.1O 2, or equivalently 0.6Li[Li1/3Mn2/3]O 2-0.4Li[Mn0.3Ni0.45Co0.25]O 2. These aspects were investigated by cyclic voltammetry studies in conjunction with electrochemical impedance spectroscopy measurements to understand the redox reactions involving multiple transition metals and their capacity contribution at higher voltages, up to 4.9 V. Further, cathodes with 1.5 wt.% carbon nanofibers added to the Li1.2Mn 0.525Ni0.175Co0.1O2 composite electrode showed stable reversible capacities of about 280 mAh g-1 when cycled to 4.9 V for more than 100 cycles, and almost a factor of two improvements in the rate performance compared to the electrode composition prepared using conventional composition (7.5% carbon black and 7.5% binder). © 2011 Elsevier B.V. All rights reserved.