The lithium-ion battery cathode material LiFePO4 doped by Er3+ was synthesized through solid-state reaction. The X-ray diffraction analysis, four-probe method, electrochemical impedance spectroscopy and galvanostatic charge and discharge performance testing were used to study the position and the quantity of doping on the crystal structures, electronic conductivity and electrochemical performance of the samples. The results have shown that the effect of doping on Fe-site is better than Li-site. The Er3+ dope of less than 3% does not affect the crystalline structure of the material but changes the microstructure of the samples when the electronic conductivity increases by four orders of magnitude. The discharge capacity of the sample is 103.47 mAh / g at the rate of 1.0 ℃, with an increase of 22.28% over the undoped samples. The doping of Er3+ improves its specific capacity, cycling and rate electrochemical properties.