Abstract: The positive material spinal LiMn₂O₄ of lithium ion battery is prepared by a modified citric acid complexation method. Its crystalline type and electrochemical properties are measured through XRD, cyclic voltammetry, charge discharge at constant current and AC impedance test. The results show that active material has different characteristic at different potential. The AC impedance spectrum is different in and off platform. Off the platform, the graph of high frequency stand for the solid diffusing of Li⁺ in the electrode material, and in the platform, the graph of high frequency stand for the impedance of the passage the electron moving to.