Electrochemical intercalation kinetics of lithium ions for spinel LiNi0.5Mn1.5O4 cathode material

Abstract

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 (Rct), surface layer capacitance, exchange current density (i0), 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 Rs is almost a constant at different states of charge. The thickness of SEI film increases with increasing of the cell voltage. Rct values evidently decreases when lithium ions deintercalated from the cathode in the voltage range from OCV to 4.6 V, and Rct value increases with increasing potential of deintercalation over 4.7 V. i0 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 cm2 s−1.