A Co-Mn-Mg co-substituted LiNi0.9Co0.05[Mn-1/2 Mg-1/2](0.05)O-2 solid solution was synthesized and characterized by XRD, XPS, SEM and its electrochemical electrochemical performance was investigated. Potato-like (similar to 15 mu m) single phase LiNi0.9Co0.05[Mn-1/2 Mg-1/2](0.05)O-2 compound was obtained and its crystal structure was analyzed by Rietveld refinements. XPS results showed that Ni, Co, Mn and Mg at the surface of LiNi0.9Co0.05[Mn-1/2 Mg-1/2](0.05)O-2 powder exist at +4, +3, +3 and +2 oxidation states respectively. And Ni in the bulk was also determined to occur as electrochemical-active Ni3+ ion, which is beneficial for high capacity electrode. The synthesized LiNi0.9Co0.05[Mn-1/2 Mg-1/2](0.05)O-2 can deliver a high initial discharge capacity of 191.5 mAhg(-1) at 0.2C rate and more than 93% of the initial specific discharge capacity was retained after 50 cycles. (C) 2012 Elsevier B.V. All rights reserved.