Monoclinic phase FePO4·2H2O nanoplates are synthesized very easily in a waterbath and are lithiated to LiFePO4/C nanoparticles by a simple rheological phase method. The thickness of the nanoplates can be tuned simply by changing the concentrations of the reactants. The LiFePO4/C nanoparticles lithiated from the thin FePO4·2H2O nanoplates, with the sizes about 50nm and the carbon coating layer at the surface 1–2nm, show excellent high-rate performance and long-term cyclability as the cathode for lithium ion batteries, delivering discharge capacities of more than 150, 120, 110, 100, and 75mAhg−1 at rates of 5C, 10C, 15C, 20C and 30C, respectively.