Li3V2(PO4)3 cathode materials were synthesized by a simple carbon-thermal reduction method using polystyrene as a carbon source. The residual carbon produced by the pyrolysis of polystyrene produced fine particle sizes and uniform carbon distribution on the Li3V2(PO4)3 particle surface. By increasing the amount of polystyrene added in the range of 0–16wt.%, the thickness of the carbon coating increased, and the coating thickness was found to influence the electrochemical performance of the Li3V2(PO4)3 significantly. Our results indicate that the 6wt.% polystyrene added Li3V2(PO4)3 with a 0.5–1nm thick carbon coating possesses the highest initial discharge capacity of 132.7mAhg−1 between 3.0 and 4.3V at 0.1C. However, at high current densities, the higher polystyrene added Li3V2(PO4)3/C with a thicker carbon coating shows better performance in terms of the discharge capacity and cycling stability than that with the thin carbon coating. The improved cycling performance at higher current densities is attributed to the relatively small particle size and the suppressed impedance increase because of the thicker carbon coating.