The phase compositions of the LiFePO4-based cathode materials upon varying the adding amount of vanadium x from 0 to 0. 13 are systemically investigated. A corresponding concentration-composition phase diagram is presented, and the x-dependent variations in the physiochemical and electrochemical performances are systemically analyzed. In the whole concentration range, the chemical valence of Fe2+ remains invariant whereas the valence of vanadium evolves from +4 to +3. With the increase of adding amount of vanadium, the electrical conductivity of samples varies nonlinearly as an "N" shape while the lithium ion diffusion coefficient first increases and then decreases. The doping of vanadium (x <= 0.07) is beneficial to refine the particle size and increase the electrical conductivity. Upon doping, the reversibility of the electrochemical reaction and the rate capability are monotonically enhanced. The conductive VO2(B) modifies the interface property of nanoparticles, and the sample achieves the high power density without sacrificing the energy density due to pesudocapacitive behavior. The formation of Li3V2(PO4)(3) (x >= 0.11) is more beneficial to improve the rate capacity of the LiFePO4-based cathode, although it undermines the lithium-ion transport of the main phase. By optimizing the content of Li3V2(PO4)(3), excellent rate capacity and high specific capacity can be achieved. (C) 2010 The Electrochemical Society.[DOI: 10.1149/1.3514688] All rights reserved.