The processes of insertion and deinsertion of lithium ion in a spinel LiMn2O4 electrode during the first charge-discharge cycle were investigated by electrochemical impedance spectroscopy (EIS). The results illustrate that the depressed semicircle in the high frequency region consists of two semicircles that are overlapped each other, and were assigned respectively to lithium-ion migration through solid electrolyte interphase (SEI) film as well as the electronic properties of the material. An appropriate equivalent circuit was proposed to fit the experimental EIS data and variations of the resistance of SEI film, the electronic resistance of the material and the resistance of charge transfer along with the increase and decrease of electrode polarization potential were quantitatively analyzed. Based on the EIS results and analysis, a physical mechanism of lithium insertion and deinsertion was suggested.

Key words: Li-ion battery, spinel LiMn2O4, SEI film, electronic conductivity, electrochemical impedance spectroscopy