Electrochemical Intercalation Kinetics of Lithium Ions for Spinel LiNi0.5Mn1.5O4 Cathode Material

The crystal structure and electrochemical intercalation kinetics of spinel LiNi0.5Mn1.5O4 such as the resistance of a solid electrolyte interphase (SEI) film, charge transfer resistance (R-ct), surface layer capacitance, exchange current density (i(0)), and chemical diffusion coefficient are evaluated by Fourier transform infrared (FT-IR) and electrochemical impedance spectroscopy (EIS), respectively. FT-IR shows that LiNi0.5Mn1.5O4 thus obtained has a cubic spinel structure, which can be indexed in a space group of Fd3m with a disordering distribution of Ni. EIS indicates that R-s is almost a constant at different states of charge. The thickness of SEI film increases with increasing of the cell voltage. R-ct values evidently decreases when lithium ions deintercalated from the cathode in the voltage range from OCV to 4.6 V, and R-ct value increases with increasing potential of deintercalation over 4.7 V. i(0) varies between 0.2 and 1.6 mA cm(-2), and the solid phase diffusion coefficient of Li+ changed depending on the electrode potential in the range of 10(-11)-10(-9) cm(2) s(-1).