The electronic structures of Mg-doped LiCoO2 have been investigated by the first-principle pseudopotential method. The effect of Mg-doping content on the band structure and structural stability of LiCoO2 is presented. The results obtained via a full relaxation of the crystalline structure show that a rational amount of Mg-doping in LiCoO2 is helpful to enhance its electronic conductivity. However, the doping magnitude should be controlled within 15 mol% of LiCoO2 in order to keep its crystalline structure unchanged. By combining total energy calculations with basic thermodynamics, the average intercalation voltages of this doped system have been predicted. (C) 2007 Elsevier B.V. All rights reserved.