The study of lithium ion de-insertion/insertion in LiMn2O4 and determination of kinetic parameters in aqueous Li2SO4 solution using electrochemical impedance spectroscopy

In this work, we report a basic study on the mechanism of lithium ion de-insertion/insertion process from/into LiMn2O4 cathode material in aqueous Li2SO4 solution using electrochemical impedance spectroscopy (EIS). An equivalent circuit distinguishing the kinetic parameters of lithium ion de-insertion/insertion is used to simulate the experimental impedance data. The fitting results are in good agreement with the experimental results and the parameters of the kinetic process of Li+ de-insertion and insertion in LiMn2O4 at different potentials during charge and discharge are obtained using the same circuit. The results indicate that the de-insertion/insertion behavior of lithium ions at LiMn2O4 cathode in Li2SO4 aqueous solution is similar to that reported in the organic electrolytes. The charge transfer resistance (Rct), warburg resistance, double layer capacitance and chemical diffusion coefficient (DLi+DLi+) vary with potentials during de-insertion/insertion processes. Rct is lowest at the CV peak potentials and the important kinetic parameter, DLi+DLi+ exhibits two distinct minima at potentials corresponding to CV peaks during de-insertion–insertion and it was found to be between 10−8 and 10−10 cm2 s−1during lithium de-insertion/insertion processes.