In order to inhibit the decomposition of the electrolytes and improve the performance of Li3V2(PO4)3 cathode materials at high potentials, we propose a conducting polymer coating method by the in situ electropolymerization of thiophene which was added to conventional organic electrolytes. The formation of polythiophene film on Li3V2(PO4)3 surface was demonstrated by high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. Polythiophene-coated Li3V2(PO4)3 cathode materials exhibited higher reversible charge/discharge capacity and better rate performance. Electrochemical impedance spectroscopy indicated that the addition of thiophene decreased the decomposition of the electrolytes on the cathode surface and improved the electronic conductivity of Li3V2(PO4)3, allowing Li+ ions in Li3V2(PO4)3 to deintercalate/intercalate more smoothly.